Fix T92930: Outliner "Show Active" bone fails in certain situations

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

source/blender/editors/object/object_utils.c

@@ -115,7 +115,7 @@ bool ED_object_calc_active_center_for_posemode(Object *ob,
                                                const bool select_only,
                                                float r_center[3])
 {
-  bPoseChannel *pchan = BKE_pose_channel_active(ob);
+  bPoseChannel *pchan = BKE_pose_channel_active_if_layer_visible(ob);
   if (pchan && (!select_only || (pchan->bone->flag & BONE_SELECTED))) {
     copy_v3_v3(r_center, pchan->pose_head);
     return true;