Refactor some code out of tile manager

[HarelM]

This introduces the InViewTiles class that stores all the tiles that are currently loaded in view.
It moves some of the logic related to these tiles to this class.
It moves the raster fade logic into another file (not a class, but just a method at this point).
It moves some methods and for loops around to better places than what they used to be.
This PR doesn't change any internal logic as far as I could see.

This is related to other PRs in this area, in order to improve the code in Tile Manager.
I couldn't find a lot of code related to vector handling that is worth a tile_manager_vector.ts file, but I might have overlooked.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov]

Codecov Report

❌ Patch coverage is 95.55556% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.40%. Comparing base (be04c90) to head (d54583b).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tile/tile_manager_raster_dem.ts	80.76%	5 Missing ⚠️
src/tile/tile_manager_raster.ts	94.80%	4 Missing ⚠️
src/tile/tile_manager.ts	98.46%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6756      +/-   ##
==========================================
+ Coverage   92.23%   92.40%   +0.17%     
==========================================
  Files         285      288       +3     
  Lines       23735    23771      +36     
  Branches     5043     5054      +11     
==========================================
+ Hits        21891    21965      +74     
+ Misses       1844     1806      -38     

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[wayofthefuture]

I gave it a good read, but can't really get into testing it as I'm out of town. Will have more time starting Wednesday. Looks good to me though... I added some slight suggestions...

[wayofthefuture]

I accidentally deleted your comment about tests fyi!

[HarelM]

Ok, I've added tests to sorting, added some checks to backfill flag to avoid doing it twice when there's no need, and added tests for that.