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.
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