[Feature branch] Prompt existing generic ZH variant users to select regional variant

[cooltey]

This PR moves the chineseLocaleToWikiLanguageCode function to AppLanguageLookUpTable and updates its logic to be:

1. Region first: get region language code from locale.country if the script is either Hant or Hans, or the language tag starts with zh-.
2. Change the default fallback language code from zh-hant to zh-tw.
3. Update test cases for the changes.

This PR should be fine to be merged into the main, or we can keep this in this ranch as a feature branch.

Bug: T360585