[PM-26292] tool: Add script to delete unused Localizable.strings entries

[KatherineInCode]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-26292

📔 Objective

This builds on #2412 by adding a module that finds unused strings and deletes them. I also did some refactoring of the strings file management into a separate python module.

I also ran the script, and it found 308 unused keys, many of which were identified in #2003. I'm not entirely sure why it's so many, especially of what seem like basic strings, though my guess is that some are used on Android, and a lot of them are detritus from MAUI or earlier that just never got cleaned up.

As noted in #2412, eventually we could have running these scripts be part of the CI process in some way, but currently these are still manual runs.

[github-actions]

Checkmarx One – Scan Summary & Details – bcb485d3-e699-45b9-ae7d-bb732dab2549

Great job! No new security vulnerabilities introduced in this pull request

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.38%. Comparing base (fdf096d) to head (f25e6b7).

❗ There is a different number of reports uploaded between BASE (fdf096d) and HEAD (f25e6b7). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (fdf096d)	HEAD (f25e6b7)
	2	1

Additional details and impacted files

@@                         Coverage Diff                         @@
##           pm-26293/delete-unused-strings    #2464       +/-   ##
===================================================================
- Coverage                           85.27%   42.38%   -42.89%     
===================================================================
  Files                                2063      585     -1478     
  Lines                              175943    31627   -144316     
===================================================================
- Hits                               150029    13406   -136623     
+ Misses                              25914    18221     -7693     

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