compositor: implement presentation_feedback

compositor: implement presentation_feedback

Implement the presentation.feedback request, and the
presentation_feedback protocol interface. Feedback information is
delivered to clients as the backend reports it, except the refresh
counter (MSC) which is always reported as zero.

Changes in v4:

* add 'flags' argument to 'presented' event without implementation

Changes in v5:

* remove the 'destroy' method implementation for feedback objects
  [Pekka Paalanen: do not leak struct feedback.]

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
v3 Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>