window-group: Set flag CLUTTER_ACTOR_NO_LAYOUT

So that moving a window (or DnD) does not trickle up and become a
full stage relayout on every frame.

This cuts the CPU requirement for dragging windows by around 20%.

GNOME/mutter!270
4 jobs for !270 with meta-window-group-no-layout in 6 minutes and 40 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Review
passed #293134
check-commit-log

00:00:45

 
  Build
passed #293135
build-mutter

00:02:25

 
  Test
passed #293137
can-build-gnome-shell

00:02:31

passed #293136
test-mutter

00:03:29