Eliminate use of nightly feature min_specialization.

The `min_specialization` feature is only available in nightly and
doesn't seem to be making progress towards becoming a supported language
feature.

What is necessary to support serde-annotate is to be able to get a
reference to the `dyn Annotate` implementation.  With
`min_specialization`, this was done by implementing a default `Annotate`
for all `T: Serialize` and then specialzing `Annotate` on types with
specific annotators.  This generally worked, but it did cause some
problems around `erased_serde::Serialize` as any type information about
the type was erased.

What is really required to implement annotations is to be able to look
up the Annotators for a given type.  The serde serializer actually helps
with this:  The serialize functions for structs and enums accept a
`name` parameter which is the typename of the item being serialized.
Instead of using `min_specialization`, we build a database mapping
typenames to casting functions that can cast a pointer to the
appropriate `dyn Annotate` reference.

1. Simplify the `Annotate` trait to only include the format and comment
   annotations.
2. Update the derive macro to only implement format/comment.  Use the
   `inventory` crate to register the name to annotator-cast functions.
3. Update tests.

Signed-off-by: Chris Frantz <frantzcj@gmail.com>

Author: Chris Frantz

.bazelrc

@@ -1 +1 @@
-build --@rules_rust//rust/toolchain/channel=nightly
+#build --@rules_rust//rust/toolchain/channel=nightly

Cargo.Bazel.lock

@@ -1,5 +1,5 @@
 {
-  "checksum": "d25b71cb8422c2cc372f8d16d141b4bde19d8572657286081c22c02b1873bfc4",
+  "checksum": "79aea2ecf9b57abcd039ca3c4a962efb4bcb38de962fd02e940aae8dd040f0c2",
   "crates": {
     "aho-corasick 1.1.3": {
       "name": "aho-corasick",
@@ -878,6 +878,53 @@
       },
       "license": "MIT OR Apache-2.0"
     },
+    "erased-serde 0.4.4": {
+      "name": "erased-serde",
+      "version": "0.4.4",
+      "repository": {
+        "Http": {
+          "url": "https://static.crates.io/crates/erased-serde/0.4.4/download",
+          "sha256": "2b73807008a3c7f171cc40312f37d95ef0396e048b5848d775f54b1a4dd4a0d3"
+        }
+      },
+      "targets": [
+        {
+          "Library": {
+            "crate_name": "erased_serde",
+            "crate_root": "src/lib.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        }
+      ],
+      "library_target_name": "erased_serde",
+      "common_attrs": {
+        "compile_data_glob": [
+          "**"
+        ],
+        "crate_features": {
+          "common": [
+            "alloc",
+            "default",
+            "std"
+          ],
+          "selects": {}
+        },
+        "deps": {
+          "common": [
+            {
+              "id": "serde 1.0.197",
+              "target": "serde"
+            }
+          ],
+          "selects": {}
+        },
+        "edition": "2021",
+        "version": "0.4.4"
+      },
+      "license": "MIT OR Apache-2.0"
+    },
     "generic-array 0.14.7": {
       "name": "generic-array",
       "version": "0.14.7",
@@ -1094,6 +1141,36 @@
       },
       "license": "Apache-2.0 OR MIT"
     },
+    "inventory 0.3.15": {
+      "name": "inventory",
+      "version": "0.3.15",
+      "repository": {
+        "Http": {
+          "url": "https://static.crates.io/crates/inventory/0.3.15/download",
+          "sha256": "f958d3d68f4167080a18141e10381e7634563984a537f2a49a30fd8e53ac5767"
+        }
+      },
+      "targets": [
+        {
+          "Library": {
+            "crate_name": "inventory",
+            "crate_root": "src/lib.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        }
+      ],
+      "library_target_name": "inventory",
+      "common_attrs": {
+        "compile_data_glob": [
+          "**"
+        ],
+        "edition": "2021",
+        "version": "0.3.15"
+      },
+      "license": "MIT OR Apache-2.0"
+    },
     "itoa 1.0.11": {
       "name": "itoa",
       "version": "1.0.11",
@@ -1620,6 +1697,167 @@
       },
       "license": "MIT OR Apache-2.0"
     },
+    "proc-macro-error 1.0.4": {
+      "name": "proc-macro-error",
+      "version": "1.0.4",
+      "repository": {
+        "Http": {
+          "url": "https://static.crates.io/crates/proc-macro-error/1.0.4/download",
+          "sha256": "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+        }
+      },
+      "targets": [
+        {
+          "Library": {
+            "crate_name": "proc_macro_error",
+            "crate_root": "src/lib.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        },
+        {
+          "BuildScript": {
+            "crate_name": "build_script_build",
+            "crate_root": "build.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        }
+      ],
+      "library_target_name": "proc_macro_error",
+      "common_attrs": {
+        "compile_data_glob": [
+          "**"
+        ],
+        "crate_features": {
+          "common": [
+            "default",
+            "syn",
+            "syn-error"
+          ],
+          "selects": {}
+        },
+        "deps": {
+          "common": [
+            {
+              "id": "proc-macro-error 1.0.4",
+              "target": "build_script_build"
+            },
+            {
+              "id": "proc-macro2 1.0.79",
+              "target": "proc_macro2"
+            },
+            {
+              "id": "quote 1.0.35",
+              "target": "quote"
+            },
+            {
+              "id": "syn 1.0.109",
+              "target": "syn"
+            }
+          ],
+          "selects": {}
+        },
+        "edition": "2018",
+        "proc_macro_deps": {
+          "common": [
+            {
+              "id": "proc-macro-error-attr 1.0.4",
+              "target": "proc_macro_error_attr"
+            }
+          ],
+          "selects": {}
+        },
+        "version": "1.0.4"
+      },
+      "build_script_attrs": {
+        "data_glob": [
+          "**"
+        ],
+        "deps": {
+          "common": [
+            {
+              "id": "version_check 0.9.4",
+              "target": "version_check"
+            }
+          ],
+          "selects": {}
+        }
+      },
+      "license": "MIT OR Apache-2.0"
+    },
+    "proc-macro-error-attr 1.0.4": {
+      "name": "proc-macro-error-attr",
+      "version": "1.0.4",
+      "repository": {
+        "Http": {
+          "url": "https://static.crates.io/crates/proc-macro-error-attr/1.0.4/download",
+          "sha256": "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+        }
+      },
+      "targets": [
+        {
+          "ProcMacro": {
+            "crate_name": "proc_macro_error_attr",
+            "crate_root": "src/lib.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        },
+        {
+          "BuildScript": {
+            "crate_name": "build_script_build",
+            "crate_root": "build.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        }
+      ],
+      "library_target_name": "proc_macro_error_attr",
+      "common_attrs": {
+        "compile_data_glob": [
+          "**"
+        ],
+        "deps": {
+          "common": [
+            {
+              "id": "proc-macro-error-attr 1.0.4",
+              "target": "build_script_build"
+            },
+            {
+              "id": "proc-macro2 1.0.79",
+              "target": "proc_macro2"
+            },
+            {
+              "id": "quote 1.0.35",
+              "target": "quote"
+            }
+          ],
+          "selects": {}
+        },
+        "edition": "2018",
+        "version": "1.0.4"
+      },
+      "build_script_attrs": {
+        "data_glob": [
+          "**"
+        ],
+        "deps": {
+          "common": [
+            {
+              "id": "version_check 0.9.4",
+              "target": "version_check"
+            }
+          ],
+          "selects": {}
+        }
+      },
+      "license": "MIT OR Apache-2.0"
+    },
     "proc-macro2 1.0.79": {
       "name": "proc-macro2",
       "version": "1.0.79",
@@ -1988,6 +2226,7 @@
         ],
         "crate_features": {
           "common": [
+            "alloc",
             "default",
             "derive",
             "serde_derive",
@@ -2049,6 +2288,14 @@
               "id": "anstyle 1.0.6",
               "target": "anstyle"
             },
+            {
+              "id": "erased-serde 0.4.4",
+              "target": "erased_serde"
+            },
+            {
+              "id": "inventory 0.3.15",
+              "target": "inventory"
+            },
             {
               "id": "num-traits 0.2.18",
               "target": "num_traits"
@@ -2154,6 +2401,10 @@
         ],
         "deps": {
           "common": [
+            {
+              "id": "proc-macro-error 1.0.4",
+              "target": "proc_macro_error"
+            },
             {
               "id": "proc-macro2 1.0.79",
               "target": "proc_macro2"
@@ -2476,6 +2727,67 @@
       },
       "license": "MIT"
     },
+    "syn 1.0.109": {
+      "name": "syn",
+      "version": "1.0.109",
+      "repository": {
+        "Http": {
+          "url": "https://static.crates.io/crates/syn/1.0.109/download",
+          "sha256": "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
+        }
+      },
+      "targets": [
+        {
+          "Library": {
+            "crate_name": "syn",
+            "crate_root": "src/lib.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        },
+        {
+          "BuildScript": {
+            "crate_name": "build_script_build",
+            "crate_root": "build.rs",
+            "srcs": [
+              "**/*.rs"
+            ]
+          }
+        }
+      ],
+      "library_target_name": "syn",
+      "common_attrs": {
+        "compile_data_glob": [
+          "**"
+        ],
+        "deps": {
+          "common": [
+            {
+              "id": "proc-macro2 1.0.79",
+              "target": "proc_macro2"
+            },
+            {
+              "id": "syn 1.0.109",
+              "target": "build_script_build"
+            },
+            {
+              "id": "unicode-ident 1.0.12",
+              "target": "unicode_ident"
+            }
+          ],
+          "selects": {}
+        },
+        "edition": "2018",
+        "version": "1.0.109"
+      },
+      "build_script_attrs": {
+        "data_glob": [
+          "**"
+        ]
+      },
+      "license": "MIT OR Apache-2.0"
+    },
     "syn 2.0.55": {
       "name": "syn",
       "version": "2.0.55",