Cleanup: Animation, move AnimData API to anim_data.c/BKE_anim_data.h

The `BKE_animsys.h` and `anim_sys.c` files already had a an "AnimData
API" section. The code in that section has now been split off, and
placed into `BKE_anim_data.h` and `anim_data.c`.

All files that used to include `BKE_animsys.h` have been adjusted to
only include the animation headers they need (sometimes none).

No functional changes.

source/blender/makesrna/intern/rna_animation.c

@@ -113,6 +113,7 @@ const EnumPropertyItem rna_enum_keying_flag_items_api[] = {
 
 #  include "BLI_math_base.h"
 
+#  include "BKE_anim_data.h"
 #  include "BKE_animsys.h"
 #  include "BKE_fcurve.h"
 #  include "BKE_nla.h"