Fix Wayland animations

This is based on the patch that @rtcm wrote for bug https://bugzilla.gnome.org/show_bug.cgi?id=780292, with the addition of 2 other patches that implement @jadahl's comment on that same bug report.

I don't have any statistics, but the number of calls to meta_window_wayland_move_resize() was brutally reduced to only 2 calls - one before and the second when calling commit.

Take this with a grain of salt: I can potentially be doing something incredibly stupidly wrong.

Issue: #78 (closed)