Add URI singleton methods

[ybiquitous]

This change adds signatures of the URI module singleton methods (and constants).
This also adds URI:RFC* modules and classes to pass the test but their content are empty still.

I refer to the following resources:

• https://ruby-doc.org/stdlib-2.7.2/libdoc/uri/rdoc/URI.html
• https://github.com/ruby/ruby/blob/v2_7_2/lib/uri/common.rb
• https://github.com/ruby/ruby/blob/v2_7_2/test/uri/test_common.rb

[ybiquitous]

Oh, I forget to add the Kernel::URI method. I'll add it soon.

[ybiquitous]

Done. (squashed)

[soutaro]

It seems like isindex and use__charset_ accepts any value, not only true and false.
boolish would be better?

[ybiquitous]

Surely, boolish is more flexible. I'll fix it soon.

[ybiquitous]

Fixed via 708bbf4

[ybiquitous]

I've rebased master and squashed to one commit.

[soutaro]

boolish looks better to me.

[ybiquitous]

By the way, does adding a Goodcheck rule below make sense? 👇

  - id: prefer_boolish_over_bool
    pattern:
      - regexp: '\([^(]*\bbool\b[^\n]*\)'
      - token: "-> bool }"
    message: |
      Prefer `boolish` over `bool` for method arguments and block return values

      See the doc below:
      https://github.com/ruby/rbs/blob/78d04a2db0f1c4925d2b13c2939868edf9465d6c/docs/syntax.md#bool-or-boolish
    glob:
      - "**/*.rbs"
    justification:
      - When the method arguments or block return values require `true` or `false` strictly.
    pass:
      - "(arg: boolish)"
      - "{ () -> boolish }"
    fail:
      - "(arg: bool)"
      - "{ () -> bool }"

According to https://github.com/ruby/rbs/blob/78d04a2db0f1c4925d2b13c2939868edf9465d6c/docs/syntax.md#bool-or-boolish.

E.g.

$ be goodcheck check -R prefer_boolish_over_bool core
core/complex.rbs:168:14: Prefer `boolish` over `bool` for method arguments and block return values
  def clone: (?freeze: bool) -> self
             ^~~~~~~~~~~~~~~
core/exception.rbs:193:21: Prefer `boolish` over `bool` for method arguments and block return values
  def full_message: (?highlight: bool, ?order: :top | :bottom) -> String
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
core/float.rbs:174:14: Prefer `boolish` over `bool` for method arguments and block return values
  def clone: (?freeze: bool) -> self
             ^~~~~~~~~~~~~~~

[ybiquitous]

I've open PR #531 to add a Goodcheck rule as a test, but please close the PR if you don't want.

[soutaro]

Thanks!