The order and way include macros were structured was chaotic, with no
real common thread between files. Try to tidy up the mess with some
common scheme, to make things look less messy.
In order to reuse some vector math for pointer confinement, move out
those parts to its own file, introducing the types old types
"MetaVector2" and "MetaLine2" outside of meta-barrier-native.c, as well
as introducing MetaBorder which is a line, with a blocking direction.
https://bugzilla.gnome.org/show_bug.cgi?id=744104
When running as a dispay server pointer barriers are a server side
feature and requires no client interaction of any sort. This patch
implements pointer barriers that can be used when running as a display
server on the native backend. Running as a display server using the X11
backend is currently not supported.
https://bugzilla.gnome.org/show_bug.cgi?id=706655
