- 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.
Fixes:
* Nuclear-purple color exploit.
* #3247.
* Removes a bunch of unnecessary color conversions every frame.
Caveats:
* The ramp range is now defined on the palette, so ramps can no longer be set per-player (may impact maps which define custom colors).
* It's no longer possible to perfectly recreate the original WW color ramps (I doubt we care).
* The old ColorRamp setting isn't migrated, so players will lose their color settings.
