No functional change.
In an attempt to fix T65671 and make a function in pose mode
equivalent to ED_armature_ebone_transform_mirror_update,
I came across the dilemma of where to put this function.
I don't know yet, but rearranging the header is a good start.
(Note to myself:
pose_transform_mirror_update is the equivalent function found in transform_generics.c)