Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.
The addition of GdkMonitor broke the quartz backend. This patch restores
that support by adding a new class GdkQuartzMonitor, and by modifying
the existing classes GdkQuartzDisplay and GdkQuartzScreen where
necessary.
It should be noted that this patch is essentially a refactor as no new
functionality that will impact the user has been added or removed.
https://bugzilla.gnome.org/show_bug.cgi?id=779184
