cogl_clip_push, and cogl_clip_push_window_rect which are now deprecated were
used in various places internally so this just switches to using the
replacement functions.
Unlike OpenGL Cogl puts the origin of windows/viewports at the top left
instead of bottom left. This test verifies that we correctly translate Cogl
viewports to OpenGL viewports for the awkward cases where the given viewport
has an offset and/or the viewport has a different size to the current draw
buffer.