Implement freezing of updates during resize

Replace the unused meta_compositor_set_updates() with
a reversed-meaning meta_compositor_set_updates_frozen(), and use
it to implement freezing application window updates during
interactive resizing. This avoids drawing new areas of the window
with blank content before the application has a chance to repaint.

https://bugzilla.gnome.org/show_bug.cgi?id=685463