[Misc] Miscellaneous code cleanup

[DayKev]

What are the changes the user will see?

N/A

Why am I making these changes?

Just purifying some heretical code. 🙏

What are the changes from a developer perspective?

• Replaced . with #app in overrides.ts imports.
• Added a missing semicolon and missing explanation comment in eslint.config.js.
• phases/move-effect-phase.ts:
  • Fix indentation
  • Renamed getTarget to getFirstTarget for clarity.
  • Converted namespace import (Utils) to named imports.
  • Added public/etc to class methods.
• field/pokemon.ts:
  • Renamed generateVariant() to generateShinyVariant() for clarity.
  • Marked various methods as public/etc.
  • Added tsdocs to isOfType().
  • Updated various tsdocs and comments (and removed an obsolete comment).
  • Cleaned up the monstrosity that was a 450+ line of code (Xavion please...) into something readable.
• utils.ts:
  • Removed an unused function randSeedEasedWeightedItem().
  • Marked IntegerHolder, FixedInt, and fixedInt() as deprecated.
  • Updated various tsdocs and comments.

How to test the changes?

Play the game normally.

Checklist

• [x] I'm using beta as my base branch
• [x] There is no overlap with another PR?
• [x] The PR is self-contained and cannot be split into smaller PRs?
• [x] Have I provided a clear explanation of the changes?
• ~[ ] Have I considered writing automated tests for the issue?~
• ~[ ] If I have text, did I make it translatable and add a key in the English locale file(s)?~
• [x] Have I tested the changes (manually)?
  • [x] Are all unit tests still passing? (npm run test)
• ~[ ] Are the changes visual?~
  • ~[ ] Have I provided screenshots/videos of the changes?~