As far as it's currently possible to implement. CompositorInterface is
able to create a surface and emits the created SurfaceInterface. It
does not yet support regions.

The SurfaceInterface is already more complete. It keeps track of the
double buffered states and emits signals when one of the values are
changed after the committing. It supports frame callbacks and has a
hook to mark the frame as rendered.

What's still missing are the regions (as it's not implemented in
CompositorInterface) and attaching the buffer as we do not yet support
creating shm buffers and pools.

The client side test is changed to use our own server and extended to
test damage and frame callback. The test needs to be extended for scale
and transform, but that is still missing in the client side
implementation.