Optionally install examples and tests

This makes it easier to test PipeWire in its "as-installed" state,
for example in an OS distribution.

The .test metadata files in ${datadir}/installed-tests/${package} are
a convention taken from GNOME's installed-tests initiative, allowing a
generic test-runner like gnome-desktop-testing to discover and run tests
in an automatic way.

The installation path ${libexecdir}/installed-tests/${package} is also
a convention borrowed from GNOME's installed-tests initiative.

In addition to the automated tests, I've installed example executables
in the same place, for manual testing. They could be separated into
a different directory if desired, but they seem like they have more
similarities with the automated tests than differences: both are there
to test that PipeWire works correctly, and neither should be relied on
for production use. Some examples are installed in deeper subdirectories
to avoid name clashes.

Signed-off-by: Simon McVittie <smcv@debian.org>

pipewire-jack/src/meson.build

@@ -70,7 +70,8 @@ if sdl_dep.found()
   executable('video-dsp-play',
     '../examples/video-dsp-play.c',
     c_args : [ '-D_GNU_SOURCE' ],
-    install: false,
+    install : installed_tests_enabled,
+    install_dir : join_paths(installed_tests_execdir, 'examples', 'jack'),
     dependencies : [jack_dep, sdl_dep, mathlib],
     link_with: pipewire_jack,
   )