No functional changes.
Move the following keyframing functions to the animrig folder
* `insert_keyframe_direct`
* `insert_keyframe`
* `delete_keyframe`
* `clear_keyframe`
In order to disentangle the code I had to move the following as well
* `delete_keyframe_fcurve`
* `visualkey_can_use`
* `visualkey_get_values`
In order to sort the functions I made 3 files (and their header counterparts)
* fcurve.cc
* keyframing.cc
* visualkey.cc
The following functions I made public so they won't get duplicated
* `update_autoflags_fcurve_direct`
* `ANIM_setting_get_rna_values`
There are public keyframing functions that
I left in the editors/animation/keyframing.cc file
I'd like to limit the scope of this refactor, and then
clean up the moved functions before moving even more over
Part of #113278
Pull Request: https://projects.blender.org/blender/blender/pulls/113503
555731f8aa