Unfortunately XKeysymToKeycode() falls short in that it coalesces keysyms
into keycodes pertaining to the first level (i.e. lowercase). Add a
ClutterKeymapX11 method (much alike its GdkKeymap counterpart) to look up
all matches for the given keysym.
Two other helper methods have been added so the virtual device can fetch
the current keyboard group, and latch modifiers for key emission. Combining
all this, the virtual device is now able to handle keycodes in further