This honors the fullscreen output request for
`xdg_toplevel_set_fullscreen` and `zxdg_toplevel_v6_set_fullscreen`.
If the request was sent before mapping, the fullscreen output request
will be retrieved from the client_pending state for the toplevel. The
output will be passed to `view_map` and if there is a workspace on the
output, the view will be placed on that workspace.
If the request comes in after being mapped, the view will be moved to
the workspace on the output (if there is one) before becoming
fullscreen.
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