[Fix #11293] Fix a false negative for Style/Documentation

[koic]

Fixes #11293.

This PR fixes a false negative for Style/Documentation when using custom macro.

The built-in macros (e.g. include, extend, prepend) and DSL like belongs_to should be treated differently. Only include, extend, and prepend will be needed to resolve #8788.

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Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

I think it will also be a good idea to update the docs to reflect more precisely what's allowed when it comes to macros, as right now the documentation is extremely basic in this regard.

[bbatsov]

@koic Ping :-)

[koic]

I'm not sure if this change should be documented. It essentially looks like #8812's bug against #8788.
This is because it seems redundant to document that extend Bar does not require comments.

module Foo
  # documentation.
  module Bar
  end

  extend Bar
end

So, I think it's clear that this cop doesn't require documentation for extend Bar.

[bbatsov]

Okay, fair enough.

[ghiculescu]

Thank you!!