Catch more offenses in Cop/StaticTranslationDefinition

What does this MR do and why?

This MR improves this cop rule to catch more translation definitions in static scope.

The new implementation has a more pessimistic approach and only considers certain cases to be allowed.

The following cases are now banned:

class Record
  validates :foo, message: _('An error')

  included do # or prepended or class_methods
    self.error_message = _('Something went wrong.')
  end
end

This 👮 is disabled for HAML lint to reduce false positives because we consider all translation definitions in HAML files to be dynamic.

Closes #348693 (closed).

Refs !89833 (comment 985700149)

How to set up and validate locally

bundle exec rubocop --only Cop/StaticTranslationDefinition

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