This allows creating the stage much earlier than it otherwise would have
been. Our initialization sequence has always been a bit haphazard, with
first the MetaBackend created, then the MetaDisplay, and inside of that,
the MetaScreen and MetaCompositor.
Refactor this out so that the MetaBackend creates the Clutter
stage. Besides the clarity of early initialization, we now have much
easier access to the stage, allowing us to use it for things such as
key focus and beyond.
These methods allow us to set and get xkbcommon keymaps as well as
locking a specific layout in a layout group.
With this, we introduce dependencies on xkeyboard-config, xkbfile,
xkbcommon-x11 and a libX11 new enough to have xcb support.
https://bugzilla.gnome.org/show_bug.cgi?id=734301
This reverts commit 3b85e4b2b9.
This breaks touch support; reverting would break wayland
(is what this patch tried to fix; we should find a better solution
that works on both).
This makes Alt+F7 / Alt+F8 work respectively under X11 nested mode.
For the native backend implementation, we'll need a special Clutter
function, so don't implement that for now.
