[Cogl] Don't delay resize on Wayland patch v3

[Neil Roberts]

After discussing this with Robert Bragg, we decided it would be better
to rename the _cogl_framebuffer_dirty function as well so that it
matches the new terminology of ‘mid scene’. We also decided to make it
explicity set the mid scene flag whenever something is added to the
journal rather than making the wayland backend flush the journal when
resizing in case we eventually want to use this flag for other
purposes as well.

Here is a third attempt at the patch.