MetaWindow.move_to_monitor() can no longer be assumed to have updated
the monitor on return, as under wayland, if the move involves a size
change, the monitor state will only be updated after the new size has
been synced with the client.
If that happens, trying to change the workspace of the moved window
fails, as it is still considered on-all-workspaces until it leaves
the secondary monitor.
It's possible to work around this by waiting for the window to actually
enter the requested monitor. That's finicky enough to warrant a helper
funtion, so add one.
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/893
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2259>
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