This is mostly a non-functional change except for
* `overlay_armature.cc` was drawing relationship lines to bone
hidden by collection logic (except that doesn't seem to work anyway,
relationship lines are drawn regardless)
* `transform_snap_armature.cc` it was possible to snap to pose bones
hidden by collection logic.
I assumed those to be oversights so I changed them in this PR.
This does *not* remove all usages of `BONE_HIDDEN_P`
and `BONE_HIDDEN_A`. Some direct access is required in
the UI and for cases where we explicitly don't want to check
collection visibility.
Part of #138482
Pull Request: https://projects.blender.org/blender/blender/pulls/139151
b690e9d4db