Outliner would frame the armature object instead of the bone if the bone
was on a hidden armature layer.
Similar to issues reported in e.g. T58068 and T80464, this is due to the
fact that `BKE_pose_channel_active` always checks for the armature layer
(and returns NULL if a bone is not on a visible armature layer).
Now propose to make this layer check **optional** (and e.g. from the
Outliner be more permissive). This also introduces
`BKE_pose_channel_active_if_layer_visible` which just wraps
`BKE_pose_channel_active` with the check being ON.
Maniphest Tasks: T92930
Differential Revision: https://developer.blender.org/D13154
d13970de86