Move code dealing with X11 MetaOutputs and related functionality to its
own file. Eventually, a MetaOutputXrandr should be introduced, based on
MetaOutput, and this commit is in preparation for that.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
This just exposes the type and the singleton getter necessary to make
it available to introspection. We'll expose more functionality as it
becomes needed.
https://bugzilla.gnome.org/show_bug.cgi?id=743745