window-actor: Freeze subsurfaces as well

In order to prevent glitches in animations, make sure we freeze all
surfaces of a window actor.

GNOME/mutter!1339
7 jobs for !1339 with subsurface-freeze in 15 minutes and 53 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Review
passed #787949
check-commit-log

00:00:25

 
  Build
passed #787950
build-mutter

00:06:27

passed #787952
build-without-native-backend-and-wayland

00:04:07

passed #787951
build-without-opengl-and-glx

00:05:42

 
  Test
passed #787954
can-build-gnome-shell

00:03:15

passed #787970
test-mutter

00:05:44

failed #787953
test-mutter

00:05:18