compositor: protocol logger

This is better than running Weston with WAYLAND_DEBUG=server:
- It is enabled on demand, no unnecessary flooding and no need to
  restart the compositor if debug was enabled.
- It prints client pointers so that messages with different clients can
  be seen apart.

Signed-off-by: Pekka Paalanen <pq@iki.fi>

parse and print message arguments in protocol_log_fn

Signed-off-by: Maniraj Devadoss <Maniraj.Devadoss@in.bosch.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>