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>

src/modules/meson.build

@@ -127,12 +127,24 @@ test('pw-test-protocol-native',
 			c_args : libpipewire_c_args,
 			include_directories : [configinc, spa_inc ],
 			dependencies : [pipewire_dep],
-			install : false),
+			install : installed_tests_enabled,
+			install_dir : installed_tests_execdir),
 	env : [
 		'SPA_PLUGIN_DIR=@0@/spa/plugins/'.format(meson.build_root()),
 		'PIPEWIRE_MODULE_DIR=@0@/src/modules/'.format(meson.build_root())
 	])
 
+if installed_tests_enabled
+  test_conf = configuration_data()
+  test_conf.set('exec', join_paths(installed_tests_execdir, 'pw-test-protocol-native'))
+  configure_file(
+    input: installed_tests_template,
+    output: 'pw-test-protocol-native.test',
+    install_dir: installed_tests_metadir,
+    configuration: test_conf
+  )
+endif
+
 pipewire_module_adapter = shared_library('pipewire-module-adapter',
   [ 'module-adapter.c',
     'module-adapter/adapter.c',