If an output is deleted, the Workspace::desktopResized() is going to
re-assign windows to the new outputs. It is done so so the workspace
re-arrangement procedure is deterministic and has concrete order.
However, with the current Window lifecycle management, it's possible
to encounter the follwing case:
- xdg_toplevel gets created on output A
- xdg_toplevel initial state is committed
- output A is removed
- a wl_buffer is attached to the xdg_toplevel, which results in a
geometry change and an output change
- Window::setMoveResizeOutput() is called, but the previous output
is a dangling pointer
CCBUG: 489632
