The modifier event was only added in v3 of the client; sending it to
older clients (e.g. GStreamer waylandsink) causes them to disconnect
immediately.
Send the older 'format' event to all clients, and only send the newer
'modifier' event to resource versions 3 or above.
https://bugzilla.gnome.org/show_bug.cgi?id=788558
Apparently my understanding of Cogl pixel formats, or at least their
use, was somewhat shaky.
Un-invert the inversion of the DRM FourCC -> Cogl pixel format mapping
when creating dmabufs from clients, fixing inverted channel ordering
seen from GL clients, e.g. gold highlights in gtk4-demo when using the
GSK GL backend when they should be blue.
https://bugzilla.gnome.org/show_bug.cgi?id=786677
