Complex rigs are built from many bones (often overlapping) that are
connected by constraints. When investigating or debugging such rigs
one often wants to switch to the target of a constraint, or a parent
bone, but it is difficult to do manually due to overlap confusion.
This patch adds a right click menu option that automatically selects
and makes the target object or bone active for UI fields where a
suitable reference is readily available.
In order for this to work for bone parent references in Pose mode,
now even disabled fields show their context menu on right click,
but it only contains manual-related options and Jump To Target.