WaylandBackend: Ignore events on unknown surfaces

[ColinKinloch]

wl_pointer enter/leave events are being processed for libdecor surfaces (they have the tag libdecor-gtk), this means the surface user_data is being miscast as CWaylandPlane.

Fixes #1445, fixes #1558, fixes #1434

[misyltoad]

Oh dear... that makes sense...

I wonder if there is a better way than this though. Any libdecor calls we can use?

[ColinKinloch]

I'm not in love with my solution either. libdecor_frame_get_wl_surface exists but it's only exposed to the plugins (cairo, gtk). I didn't see anything particularly useful in the api.

The offending surface always seems to be wl_surface#44.

It's also possible that I'm wrong about it being libdecor, I would have thought I'd run into this when adding it to RetroArch.

[ColinKinloch]

SDL uses wl_proxy_set_tag if that's a solution you'd prefer?
https://github.com/libsdl-org/SDL/blob/main/src/video/wayland/SDL_waylandvideo.c#L391

[ColinKinloch]

This is an alternative using wl_proxy_set_tag master...ColinKinloch:gamescope:pointer_enter_crash_tag

[misyltoad]

wl_proxy_set_tag looks much better :)

[ColinKinloch]

Great.
I switched the branch and fixed the formatting to match the project.