`from_raw_parts()` is only sound if the alignment is the same, so it
can't be used to covert to a `Vec<u8>` from a type with a greater
alignment.
This isn't hard to avoid, luckily.
This fixes an issue with `cosmic-panel` where, when a workspace is moved
back to an output after a monitor is disconnected and reconnected, the
panel doesn't hide because `cosmic-panel` thinks no toplevel is open on
that monitor.
After some testing, it seems `output_enter` isn't being sent here. In
particular, the `output_leave` call happens before the client binds the
`wl_output`, so there is no `wl_output` to send in an event yet.
This is addressed by keeping track of a set of `wl_output`s that we have
sent the event to. So if an output is bound, `refresh` can add it to
this list and send the event.
This is not needed for workspaces (though it could be done similarly)
since the handle objects are created by server events. So no race should
occur as long as the workspaces global is bound before the toplevel info
one.
