Bump pub

New commits included:
```
> git log --format="%C(auto) %h %s" 0e657414a472e74ca5dd76ae0db50cc060251dec..255a3091fc278b04be74d246a3bec8743ef4d0b7
 255a3091 Vendor package:tar and package:chunked_stream (#2932)
 86bf8b20 Handle relative git-url-paths correctly when --directory (#2919)
 3716a681 Let `pub add` fail if extra arguments are passed (#2927)
 a03ac729 Minor cleanup to reduce risk of using path.current (#2924)
 e87b7b66 Added null check for name in UserInfo class (#2918)
 056a8c9a pub deps --json (#2896)
 53a69e27 Fix .packages entries of relative path deps when using --directory (#2916)
 d6308efc pub upgrade command shows count of discontinued packages (#2908)
 51744805 Upgrade to the null safe versions of all dependencies (#2913)
 e0d538c7 Introduce .pubignore (#2787)
 79f3a8b9 pub outdated: added clear message when no outdated packages. (#2898)
 22463872 `cache clean` (#2904)
 11e7b2ce `publish --dry-run` informs that the server might do more checks (#2883)
 b6977d50 Remove untrue assert (#2884)
 35841f8d Merge branch 'cherry_picks_for_2_12'
 0db3255b Don't fail on failed status listing (#2877)
 53e8ecca Don't allow outdated taking arguments (#2872)
 e83a1dc1 Enable asserts when testing pub (#2754)
 178f2edb Add --directory option (#2876)
 5aadb70e Don't fail on failed status listing (#2877)
 4bf8a927 Remove unused field (#2878)
 73ad5426 Don't allow outdated taking arguments (#2872)
 9a70949e Use Dart library to read and write tar files (#2817)
 2f74230c Do not recommend decativating packages (#2871)
 b1697a27 Use full error message string in CommandResolutionFailedException (#2870)
 16a6210d Upgrade `downgrade --help`: `downgrade` actually updates `pubspec.lock` (#2859)
 6e240ea9 Use cached version listings as heuristic when prefetching (#2851)
 58152f7c Allow trailing slash in PUB_HOSTED_URL (#2856)
 b1bf9a33 Handle poor package-listing responses robustly. (#2847)
 d941bd24 Fix request metadata when overriding dependencyType (#2848)
 ```

Change-Id: Id6ed5698330fc0cdb507e024eabc34f925ca9208
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/192304
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>
Reviewed-by: Jonas Jensen <jonasfj@google.com>

Author: sigurdm

CHANGELOG.md

@@ -36,6 +36,34 @@ Updated the Linter to `1.1.0`, which includes:
 - new lint: `use_named_constants`.
 - deprecation of `avoid_as`.
 
+### Pub
+
+* `dart pub publish` now respects `.pubignore` files with gitignore-style rules.
+ `.gitignore` files in the repo are still respected if they are not
+  overridden by a `.pubignore` in the same directory.
+
+  pub no longer queries git for listing the files. This implies:
+  * Checked in files will now be ignored if they are included by a `.gitignore`
+    rule.
+  * Global ignores are no longer taken into account.
+  * Even packages that are not in git source control will have their
+    `.gitignore` files respected.
+
+* New flag `dart pub deps --json` gives a machine parsable overview of the
+  current dependencies.
+* New command: `dart pub cache clean`. Will delete everything in your current
+  pub cache.
+* Commands related to a single package now takes a `--directory` option to
+  operate on a package in the given directory instead of the working directory.
+* git dependencies with a relative repo url would previously be interpreted
+  relative to the current package, even for transitive dependencies. This now
+  fails instead.
+
+* Pub now uses a Dart library to read and write tar files.
+  This should fix several issues we had with incompatibilities between different
+  system `tar`s.
+* `PUB_HOSTED_URL` can now include a trailing slash.
+
 ## 2.12.2 - 2021-03-17
 
 This is a patch release that fixes crashes reported by Flutter 2 users (issue

DEPS

@@ -136,7 +136,7 @@ vars = {
   "pool_rev": "7abe634002a1ba8a0928eded086062f1307ccfae",
   "process_rev": "56ece43b53b64c63ae51ec184b76bd5360c28d0b",
   "protobuf_rev": "0d03fd588df69e9863e2a2efc0059dee8f18d5b2",
-  "pub_rev": "0e657414a472e74ca5dd76ae0db50cc060251dec",
+  "pub_rev": "255a3091fc278b04be74d246a3bec8743ef4d0b7",
   "pub_semver_rev": "f50d80ef10c4b2fa5f4c8878036a4d9342c0cc82",
   "resource_rev": "6b79867d0becf5395e5819a75720963b8298e9a7",
   "root_certificates_rev": "7e5ec82c99677a2e5b95ce296c4d68b0d3378ed8",
@@ -156,6 +156,7 @@ vars = {
   "stream_channel_tag": "d7251e61253ec389ee6e045ee1042311bced8f1d",
   "string_scanner_rev": "1b63e6e5db5933d7be0a45da6e1129fe00262734",
   "sync_http_rev": "b59c134f2e34d12acac110d4f17f83e5a7db4330",
+  "tar_rev": "b59c134f2e34d12acac110d4f17f83e5a7db4330",
   "test_descriptor_tag": "2.0.0",
   "test_process_tag": "2.0.0",
   "term_glyph_rev": "6a0f9b6fb645ba75e7a00a4e20072678327a0347",