GdkFrameClock: Make the phase explicit when requesting the frame

GdkFrameClock: Make the phase explicit when requesting the frame

Instead of having gdk_frame_clock_request_frame() have
gdk_frame_clock_request_phase() where we can say what phase we need.
This allows us to know if we get a frame-request during layout whether
it's just a request for drawing from the layout, or whether another
layout phase is needed.

https://bugzilla.gnome.org/show_bug.cgi?id=685460