clients/simple-egl: Handle buffer scale and transform

Buffer scale is common enough in the modern desktop space to expect average GL clients to handle it. Thus lets include it into our main example client.

While on it, also handle buffer transforms. It's essentially free for GL clients in terms of computing power but may increase the chance that Wayland compositors are able to hit scanout fast paths. Thus having an example client for it is likely valueabel for client and compositor developers.

Signed-off-by: Robert Mader robert.mader@collabora.com