clutter: Switch to storing device->actor associations in ClutterStage

As planned and prepared with the last commits, let ClutterStage take
care of tracking input devices and their respective actors. This means
we now can remove the old infrastructure for this from
ClutterInputDevice.

Part-of: <GNOME/mutter!1633>
13 jobs for device-actors-stage
Status Job ID Name Coverage
  Review
manual #1047583
manual
check-commit-log
manual #1047584
manual
check-merge-request
 
  Prepare
created #1047586
aarch64
build-fedora-container@aarch64
created #1047585
build-fedora-container@x86_64
 
  Build
created #1047588
aarch64
build-mutter@aarch64
created #1047587
build-mutter@x86_64
created #1047590
build-without-native-backend-and-wayland@x86_64
created #1047589
build-without-opengl-and-glx@x86_64
 
  Test
created #1047593
can-build-gnome-shell@x86_64
created #1047592
aarch64
test-mutter@aarch64
created #1047591
test-mutter@x86_64
 
  Coverage
created #1047595
aarch64
test-mutter-coverage@aarch64
created #1047594
test-mutter-coverage@x86_64