VLC supports groups where mp4 defines switch groups.
As an es can't belong to multiple groups, but does in
switch groups, we don't really have a way to provide
the same track exclusion/alternative features without
duplicating es.

Priorities are then set in a way es/tracks from the same
cat/switchgroup are not all selected.

refs #3970

Follow the spec and correctly handle text encoding

And fix reading

And enforce handler

Those two callbacks only exist in wl_output version 2. VLC uses
version 1 only so far.

In practice, video output display plugins return an error when they do
not support arbitrary sizes. However nowadays, this control is requested
only when the video output or the video window report a change of size.
That cannot be allowed to fail: the display size is what it is
regardless of the result of the control request.

This enables OpenGL/OpenGL ES through Wayland.