Move the contents of `ANIM_bone_collections.h` into its C++ `ANIM_bone_collections.hh` sibling. Blender is C++ by now that we can do without the C header. No functional changes.
Move the contents of `ANIM_bone_collections.h` into its C++ `ANIM_bone_collections.hh` sibling. Blender is C++ by now that we can do without the C header. No functional changes.