Notifying Present about events' states was done prior with the single function
present_wnmd_event_notify just like in screen mode. But it is more intelligible
if at least in window mode we make use of three different functions with names
that directly indicate what their purpose is:

* present_wnmd_event_notify only for queued events feedback.
* present_wnmd_flip_notify for when a presentation occured (flip).
* present_wnmd_idle_notify for when the Pixmap of the event can be reused.

This is an API-breaking change in regards to window mode. DDX written against
the previous version won't work anymore. It is assumed that there only exists
the XWayland DDX at the moment using the window mode such that this is not an
issue for the overall ecosystem.

Signed-off-by: Roman Gilg <subdiff@gmail.com>