Added new cop - Naming/AsciiConstants

[pjskennedy]

This adds a new cop: Naming/AsciiConstants

This is an attempt to implement #7458

Rubocop currently has Naming/AsciiIdentifiers which correctly adds offenses to ruby identifiers (tIDENTIFIER) containing non-ascii characters. I find that the same rigor should be applied to constants (tCONSTANT) as the following are currently not offenses:

class Foö
end

module Foö
end

FOÖ = "foo"

---

• 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 to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• 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.

[bbatsov]

The proposed cop is fine by me. @rubocop-hq/rubocop-core any objections to including it enabled by default?

[koic]

Both this cop and Naming/AsciiIdentifiers cop conform to The Ruby Style Guide's "English Identifiers" rule. And It seems that most implementations overlap with Naming/AsciiIdentifiers cop.
https://github.com/rubocop-hq/ruby-style-guide#english-identifiers

I think there is a way to enhance the Naming/AsciiIdentifiers cop instead of creating a new cop.
So, for example, it may be better to provide ascii_constants: true (default) option or ascii_constants: false (default) option.

[bbatsov]

@koic I like this idea!

[bbatsov]

@pjskennedy I'll close this PR, so we can pursue @koic's idea. Thanks for your contribution, though.