tests/stage-views: Test whether stage views and frame clocks are freed

Add a test case to check whether the stage views and frame clocks are
all correctly freed after working with timelines a bit and then
hotplugging and removing all monitors.
13 jobs for fix-frame-clock-leak
Status Job ID Name Coverage
  Review
manual #1044203
manual
check-commit-log
manual #1044204
manual
check-merge-request
 
  Prepare
created #1044206
aarch64
build-fedora-container@aarch64
created #1044205
build-fedora-container@x86_64
 
  Build
created #1044208
aarch64
build-mutter@aarch64
created #1044207
build-mutter@x86_64
created #1044210
build-without-native-backend-and-wayland@x86_64
created #1044209
build-without-opengl-and-glx@x86_64
 
  Test
created #1044213
can-build-gnome-shell@x86_64
created #1044212
aarch64
test-mutter@aarch64
created #1044211
test-mutter@x86_64
 
  Coverage
created #1044215
aarch64
test-mutter-coverage@aarch64
created #1044214
test-mutter-coverage@x86_64