This new interface will be used by the control center and possibly
the settings daemon to configure the screens. It is designed to
resemble a simplified XRandR, while still exposing all the quirks
of the hardware, so that the panel can limit the user choices
appropriately.
To do so, MetaMonitorMode needs to track CRTCs, outputs and modes,
so the low level objects have been decoupled from the high-level
MetaMonitorInfo, which is used by core and API and offers a simplified
view of HW, that hides away the details of what is cloned and how.
This is still not efficient as it should be, because on every
HW change we drop all data structures and rebuild them from scratch
(which is not expensive because there aren't many of them, but
at least in the XRandR path it involves a few sync X calls)
https://bugzilla.gnome.org/show_bug.cgi?id=705670
Consolidate all places that deal with output configuration in
MetaScreen, which gets it either from XRandR or from a dummy static configuration.
We still need to read the Xinerama config, even when running xwayland,
because we need the indices for _NET_WM_FULLSCREEN_MONITORS, but
now we do it only when needed.
https://bugzilla.gnome.org/show_bug.cgi?id=705670
