remove tank paradrop icon
Remove redundant FindActorsInBox helpers.
Add World parameter to Target.FromOrder.
Add World parameter to Target.FromCell.
Add World parameter to Util.BetweenCells.
Replace CPos.CenterPosition -> Map.CenterOfCell.
Remove WVec.ToCVec.
Replace WPos.ToCPos -> Map.CellContaining.
Remove conversions between legacy and world types.
Remove CVec -> WVec conversion.
Changes ISpriteSource.Frames to be of type IReadOnlyList<ISpriteFrame>.

- Updated implementations to return a ReadOnlyList around an array (to reduce wasted memory from exposing lists or lazy enumerators around lists).
- Protect non-public ISpriteFrame classes by making them inner classes to prevent casting.
- Added an AsReadOnly extension method for lists.
Changed HardwarePalette.ApplyModifiers to be more efficient.

- Add separate ImmutablePalette and MutablePalette classes since the distinction is extremely important to HardwarePalette.
- Keep a cache of palettes in HardwarePalette to avoid reallocation them every time ApplyModifiers is called.
- Palettes that are not allowed to be modified are copied to the buffer once when added, rather than every time ApplyModifiers is called.
- The AdjustPalette method now takes a read-only dictionary to prevent the dictionary being messed with.
- Added a constant for the palette size to remove its usage as a magic number in several areas.
- The ColorPreviewManagerWidget is annoying in that it needs to actually permanently update a palette after it has been added. To allow this, HardwarePalette now allows a palette to be replaced after initialization. The WorldRenderer therefore now also updates the PaletteReference it created earlier with the new palette to prevent stale data being used elsewhere.
Merge pull request #5406 from RoosterDragon/palette-efficiency

Changed HardwarePalette.ApplyModifiers to be more efficient.
Merge pull request #5752 from Mailaender/tank-paradrop

Removed the tank paradrop icon
Merge pull request #5758 from pchote/cell-world-conversions

Generalize cell/world coordinate conversions.
new check for undefined actors
remove legacy actors as a test case
now that we check actors and players we can't exclude them
and another hit for invalid players
don't spam passed checks