[1.20.2] Compress the `entity` library and rename the `entity` module to `entity_extensions`

[TheGlitch76]

The entity library had way too many 1 or 2 class modules. This compresses most of those modules into the entity_extensions library (renamed from entity to match block_extensions et al).

I feel that this structure more closely follows the size and scope of modules in our other libraries (and the kind of size we want overall), but I'm absolutely open to feedback on reverting parts or organizing it differently.

[TheGlitch76]

Ennui, I disagree--QuiltExtendedSpawnDataEntity is the definition of an entity extension, and the code footprint is pretty small.

[EnnuiL]

Ennui, I disagree--QuiltExtendedSpawnDataEntity is the definition of an entity extension, and the code footprint is pretty small.

hm, fair enough

[OroArmor]

This was merged in manually