libs: window: wayland: destroy all wayland buffers during finalize

Some buffers and the associated FrameState state may still be pending at
that point. If the wayland connection is shared, then messages for the
buffer may still arrive. However, the associated event queue is already
deleted. So the result is a crash.

With a private connection the associated memory is leaked instead.

Part-of: <gstreamer/gstreamer-vaapi!342>
17 jobs for !342 with wayland-overlay in 16 minutes and 10 seconds (queued for 2 seconds)
merge request