Offer case locale specific case manipulation

[aliismayilov]

Ruby String offers few rules for case manipulation: https://docs.ruby-lang.org/en/3.4/case_mapping_rdoc.html

It would be great being able to utilize I18n to do locale aware case manipulation. For example:

# given tr.yml
# tr:
#   i18n:
#     case_map:
#       rules: turkic

I18n.upcase("Türkiye")
=> "TÜRKIYE"

I18n.locale = :tr
I18n.upcase("Türkiye")
=> "TÜRKİYE"

This would greatly improve ergonomics when working with ruby code that supports Azerbaijani and Turkish languages, whereas both support:

• ı - lowercase i without dot
• İ - uppercase i with dot