ClutterInputFocus is an abstract object to be subclassed by UI actors and
the wayland interface and represents the user of an input method. It
represents the current focus of the input method, so all emitted signals
and public API hooks are expected to be called when the input method is
currently interfacing with the input focus.

ClutterInputMethod is an abstract class (to be implemented in the upper
layers) that represents the input method itself. Besides focus management
itself, all public API calls that would be called by the subclasses are
delivered through the current input focus.