Slice experience orbs and moon phases

[muzikbike]

With 1.20.5's long-awaited splitting of map icons into individual files, this means that the only two classic-style texture atlases yet to be split are experience orbs and moon phases. Since there's just two of them, why not rip this bandaid off and get them split just before 1.20.5 releases to limit any subsequent migrations needed by resource pack authors?

Changes:

• The file assets/minecraft/textures/entity/experience_orb.png is now split into eleven texture files, one for each orb, in assets/minecraft/textures/experience_orb
• The file assets/minecraft/textures/environment/moon_phases.png is now split into eight texture files, one for each phase, in assets/minecraft/textures/celestial_body
• The file assets/minecraft/textures/environment/sun.png has been automatically moved to assets/minecraft/textures/celestial_body alongside the split moon phases

There would be two new atlases generated to deal with these newly split textures - one for experience orbs and another for all celestial bodies (the sun and all phases of the moon).

Obviously a commit like this is probably trivial compared to the code changes needed in the actual game to support split textures like these, but in the slim event that this does happen I hope I've made the process just a bit smoother for all involved. I would have done this a month ago, but #10 was a blocker.

Some things to note that may be relevant:

• The sun and moon are rendered mirrored in-game compared to their actual textures (https://bugs.mojang.com/browse/MC-241036) - it may be a good idea to have slicer output flipped versions of these textures if that bug is fixed in the same version that splits these atlases.
• I'm not sure if transferring the experience orbs' rendered translucency and color animation to the texture files themselves and using proper texture animation with json files and such would also be relevant, or if those would be better off left hardcoded.

[Gegy]

Hi - thank you for taking the time to put this PR together! We will however not be accepting this change, as it is migrating to a resource pack format that the game client does not expect, and this work is not currently planned.