Make names related to animations more consistent

[tom-overton]

There was a ton of inconsistency in the repo regarding animations, so I tried to give it a cleanup and make it consistent. I made the following changes:

• For actor struct vars, I always use animIndex or some variation of it.
• For enum values, I always use ANIM, not ANIMATION
• For enum names, I mostly use BlahAnimation. The exception is in EnNiw, because I don't quite fully understand it yet.
• For functions that change the current animation, I went with Blah_ChangeAnim
• For static data, I went with sAnimationInfo, sAnimations, and sAnimationModes

I also did some minor cleanup because I noticed some animation enums in headers that didn't need to be there, so I moved them to C files.

[tom-overton]

I standardized on Blah_ChangeAnim, as Dragorn's linked PR does too.

[hensldm]

Petrie just found a typo in SkelAnime_InterpFrameTable, where the arg tactoret should really be target which seems in scope to fix in this PR. Also I just thought of the three general animation changers Actor_ChangeAnimationByInfo, SubS_ChangeAnimationByInfoS, and SubS_ChangeAnimationBySpeedInfo which looks like they need their arg names made consistent.