When a geometry element is selected and then hidden using the visibility
checkbox in the Elements panel, it remains in the selection.
Subsequently, if another geometry element is selected and deleted, both
the visible element AND the hidden element are deleted.
Root cause of that is basically that `changeLayer()` functions change
the geometry's visual layer, but never clear the geometry from
`Gui::Selection()`.
So, this patch adds the handling to collect every sub-element name of
the hidden geometry and then formats it and calls remove selection on
the geometry during layer change transaction.
5f6e23181b