The cogl tests need to run with a display server set, however since we
use TestEnvironment, only the listed env variables will be exposed to
the test and so no DISPLAY will be set when launching it with
gnome-desktop-testing-runner.
As per this, just run the tests using xvfb-run so that we match what's
happening in CI and we ensure that the tests are run in a safe
environment.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1876>
This is the last remaining feature necessary to achieve
parity with the Autotools build.
A few changes were made to the install locations of the
tests, in order to better acomodate them in Meson:
* Tests are now installed under a versioned folder (e.g.
/usr/share/installed-tests/mutter-4)
* The mutter-cogl.test file is now generated from an .in
file, instead of a series of $(echo)s from within Makefile.
Notice that those tests need very controlled environments
to run correctly. Mutter installed tests, for example, will
failed when running under a regular session due to D-Bus
failing to acquire the ScreenCast and/or RemoteScreen names.
