Consolidate sprite anim subsystems

[mid-kid]

The two subsystems are structured as follows:

Overworld:

• data/sprite_anims/sequences.asm:SpriteAnimSeqData contains each SPRITE_ANIM_INDEX_* entry, and references:
  • data/sprite_anims/framesets.asm:SpriteAnimFrameData containing each SPRITE_ANIM_FRAMESET_* entry
  • engine/gfx/sprite_anims.asm:DoAnimFrame containing each SPRITE_ANIM_SEQ_* entry
  • The SPRITE_ANIM_DICT_* dictionary entries for the base sprite offset
• engine/gfx/sprites.asm:DoNextFrameForAllSprites contains the update loop for the objects.

Battle:

• data/battle_anims/objects.asm:BattleAnimObjects contains each ANIM_OBJ_* entry, and references:
  • data/battle_anims/framesets.asm:BattleAnimFrameData containing each BATTLEANIMFRAMESET_* entry
  • engine/battle_anims/functions.asm:DoBattleAnimFrame containing each BATTLEANIMFUNC_* entry
  • The ANIM_GFX_* dictionary entries for the base sprite offset
• engine/battle_anims/anim_commands.asm:BattleAnim_UpdateOAM_All contains the update loop for the objects.

This is quite the disarray for two subsystems that are so strikingly similar. I'd propose a few changes:

• Make the formatting of the constants match, BATTLE_ANIM_X or SPRITEANIMX
• Consolidate "sequence" vs "function" naming.
• data/sprite_anims/sequences.asm:SpriteAnimSeqData should be data/sprite_anims/objects.asm:SpriteAnimObjects
• Similarly, ANIM_OBJ_* vs SPRITE_ANIM_INDEX_*. Make the two resemble eachother.
• engine/gfx/sprite_anims.asm:DoAnimFrame -> engine/gfx/sprite_anims.asm:DoSpriteAnimFrame maybe
• Reflect the layout of engine/gfx/sprites.asm (look for INCLUDE) in engine/battle_anims/*.asm, for example like this. I wouldn't be surprised if both subsystems were originally held in a single file.
• Similarly, move engine/gfx/sprites.asm and engine/gfx/sprite_anims.asm into engine/sprite_anims/core.asm and engine/sprite_anims/functions.asm, respectively.
• probably more I can't think of right now.