gtk3: add randr 1.5 monitor support

gtk3: add randr 1.5 monitor support

This patch introduces support for using the newly introduced
monitor objects in the XRandR protocol. These objects are meant
to be used to denote a set of rectangles representing a logical
monitor, and are used to hide details like monitor tiling and
virtual gpu outputs.

This uses the new objects instead of crtc/outputs objects when
they are available to create the monitor lists. X server 1.18
is required on the server side for randr 1.5.

https://bugzilla.gnome.org/show_bug.cgi?id=749561