Update Hong Kong holidays: add l10n support

[PPsyrius]

Proposed change

• Adds Hong Kong English (en_HK), American English (en_US), Traditional Chinese (zh_HK), Simplified Chinese (zh_CN), Thai (th) localization support - with zh_HK as the new default l10n option.
• Fixes Hong Kong 🇭🇰 's Remembrance Day being mistranslated as Taiwan 🇹🇼 's "Peace Memorial Day" for English l10ns.

Note

I'm using zh_HK instead of zh_TW for Hong Kong's Traditional Chinese l10n for now since I'm not sure if both Taiwanese and Hong Konger ones are the same or not.

Type of change

• New country/market holidays support (thank you!)
• Supported country/market holidays update (calendar discrepancy fix, localization)
• Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• Dependency update (version deprecation/pin/upgrade)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (a code change causing existing functionality to break)
• New feature (new holidays functionality in general)

Checklist

• I've followed the contributing guidelines
• I've successfully run make check, all checks and tests are green

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (915dafb) to head (39f8568).

Additional details and impacted files

@@            Coverage Diff            @@
##               dev     #2268   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          199       199           
  Lines        12144     12148    +4     
  Branches      1731      1731           
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+ Hits         12144     12148    +4     

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[KJhellico]

@PPsyrius, great work! 👍 When I worked on Hong Kong last time, I tried to leave comment with Chinese name for all holidays, with the aim of l10n. I hope this was helpful.
Just a few suggestions:

[sonarqubecloud]

Quality Gate failed

Failed conditions
6.5% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[PPsyrius]

At some point, we’ll likely need to implement support for ISO-3166-2:CN for Hong Kong and Macau (the latter of which I’m currently working on).

Since each has a distinct default_language code, rather than merging them into the CN file and treating HK and MO as stub entities - like the approach proposed in #1852 for the Netherlands; we should instead look for ways to directly reference another ISO 3166-1-level entities.