window-actor/x11: Update shape even when frozen

On Xwayland, freezing actor updates on sync requests means the
server-side frame and shadows repaint will be frozen as well, which
causes the shadow to show black at times when resizing X11 clients
which support NET_WM_SYNC.

Using freeze/thaw commits prevents the content from changing, yet the
shape window still needs to be updated when frozen otherwise the
difference in shape induced by the on-going resize operation will show
as well, even if the toplevel window has its commits frozen.

GNOME/mutter!942
Closes: https://bugzilla.gnome.org/show_bug.cgi?id=767212
Closes: GNOME/mutter#858
5 jobs for !942 with set-allow-commits in 7 minutes and 45 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #556829
check-commit-log

00:00:46

 
  Build
passed #556830
build-mutter

00:03:31

passed #556831
build-without-native-backend-and-wayland

00:03:02

 
  Test
passed #556833
can-build-gnome-shell

00:01:53

passed #556832
test-mutter

00:03:27