[gui] App localizations

[sharder996]

This PR extracts the various user facing strings out of the Dart source code and places them in a dedicated resource file which provides several benefits:

• Easy access, and additional descriptive information for translators
• Eliminate code rebuilds on string edits

Localization is handled by the l10n package and is the canonical Flutter method of internationalizing Flutter apps. Additional localizations are placed under **/lib/l10n/* where localization files are generated during the build process.

For more info, see:

• https://docs.flutter.dev/ui/internationalization

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.45%. Comparing base (ed9632c) to head (40c77fa).
⚠️ Report is 207 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4797   +/-   ##
=======================================
  Coverage   87.45%   87.45%           
=======================================
  Files         258      258           
  Lines       14094    14094           
=======================================
  Hits        12324    12324           
  Misses       1770     1770           

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[sharder996]

Requesting a review from @geoffreynyaga as this is kinda related to documentation. Curious if there is a company wide standard for how to handle localization.