No correction for errors.details[:n] << v

[BrianHawley]

Fixes for Rails/DeprecatedActiveModelErrorsMethods:

• Fixed a bad autocorrection of errors.details[:name] << value.
  There isn't really a correct replacement for this one.
• Did some refactors prompted by rubocop complaints.
• Fixed a misspelling of autocorrectable.
• Added missing correction assertions to test cases.

---

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.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[BrianHawley]

You can do errors.add(:name, value) as a replacement for errors.messages[:name] << value but there's no equivalent action for errors.details[:name] << value without including the message, so it seemed safer to not correct it.

Maybe we should add an example of a correction using errors.add to replace both changing the messages and details?

This can be done as a later doc PR, if need be.

[BrianHawley]

@koic as requested.

[koic]

@BrianHawley Can you rebase with the latest master branch?

[BrianHawley]

@koic rebased.

[koic]

That just my two cents. Can you tweak it?

Suggested change

	receiver = node.receiver.receiver
	!AUTOCORRECTABLE_METHODS.include?(node.method_name) || (
	receiver&.send_type? && receiver&.method?(:details) && node.method?(:<<)
	)
	return true unless AUTOCORRECTABLE_METHODS.include?(node.method_name)
	return false unless (receiver = node.receiver.receiver)
	receiver.send_type? && receiver.method?(:details) && node.method?(:<<)

[BrianHawley]

@koic sure, done.

[koic]

Thanks!