Invoke event correctly when using deep copy on vtkBoneWidgets

When using deep copy, the bone event must also be invoked in order for the
armature (for example) to be correctly updated.

See Issue #13907
Merge branch '13907-GUIModifiedObjectChildrenUpdate' into armatures

* 13907-GUIModifiedObjectChildrenUpdate:
  Invoke event correctly when using deep copy on vtkBoneWidgets