Make ReadWriteAttribute cop aware of shadowing methods

[Drenmi]

Background

Sometimes you might want to put a method "in front of" an attribute. In this case, that method will shadow the attribute name, and using self[:foo] within the method will be an infinite loop.

Example:

class Foo < ApplicationModel
  attribute :foo

  def foo
    bar || self[:foo]
  end

  def bar
    nil
  end
end

foo = Foo.new(foo: 1)
#=> (irb):11:in `foo': stack level too deep (SystemStackError)

What is this change?

This PR makes it so that no offense is registered if #read_attribute is used in a method named after that attribute. Same for #write_attribute if called inside a writer method (suffix =) of the same name.

---

Before submitting the PR make sure the following are checked:

• 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.
• 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.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[koic]

Can you add this acceptance case to the cop's doc?

[koic]

@Drenmi Ping :-)

[pirj]

@Drenmi Ping

[Drenmi]

@koic @pirj Thanks for the wait. Rebased and incorporated suggestions. 🙂

[koic]

Thanks!