Ensure initial relayout happens for children of hidden cloned actor

From the main commit:

In certain edge cases it's currently possible that an actor never
gets a valid allocation and paint volume.

One such case is adding an unmapped, hidden child to an unmapped
cloned parent and then showing the child. This happens currently
 e.g. if a Wayland subsurface is added to a already mapped window
while the user is in the overview.

Ensure relayouts in two more such cases.

And some more fixes that should help with correctness and make debugging easier.

Closes #1726 (closed) Closes #2350 (closed) Closes #2114 (closed)

Related !2507 (closed)