[Fix #12842] Add new Style/StaticSend cop

[koic]

Fixes #12842.

Summary

Detects the use of the public_send method with a static method name argument. Since the send method can be used to call private methods, by default, only the public_send method is detected.

# bad
obj.public_send(:static_name)
obj.public_send('static_name')

# good
obj.static_name

Safety

This cop is not safe because it can incorrectly detect based on the receiver. Additionally, when AllowSend is set to true, it cannot determine whether the send method being detected is calling a private method.

AllowSend option

This cop has AllowSend option.

AllowSend: true (default)

# good
obj.send(:static_name)
obj.send('static_name')
obj.__send__(:static_name)
obj.__send__('static_name')

AllowSend: false

# bad
obj.send(:static_name)
obj.send('static_name')
obj.__send__(:static_name)
obj.__send__('static_name')

# good
obj.static_name

---

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 like the cop, but I'm not sure about the name. Perhaps this cop should consider constants as well (e.g. METHOD_NAME).

[Earlopain]

I don't think this cop should concern itself with constants (at least by default). Surely I used a constant to intentionally factor it out, unless the constant is referenced only once I'd want to keep it.

[koic]

Since a constant is generally immutable by definition, I think it can always be targeted without needing options. Are there any valid cases for excluding a constant?

[Earlopain]

There are barely any cases I could find that use public_send over send for this (send is just so much more used). This is basically what I was thinking about: https://github.com/hopsoft/turbo_boost-commands/blob/9b4535ca0fe17481e70ae292d03db5b3e984d376/test/application_system_test_case.rb#L11

It uses a constant to have one place that holds which browser is being tested. I don't believe the code will improve by calling the method directly.