meson: Add an appdata and a validation test

This adds an appdata, installs it and adds a test to validate it.

data/meson.build

@@ -11,6 +11,18 @@ if desktop_utils.found()
     )
 endif
 
+# Appdata file
+install_data('sm.puri.Calls.appdata.xml',
+    install_dir: join_paths(datadir, 'metainfo'),
+)
+
+appstream_util = find_program('appstream-util', required: false)
+if appstream_util.found()
+    test('Validate appstream file', appstream_util,
+        args: ['validate-relax', 'sm.puri.Calls.appdata.xml']
+    )
+endif
+
 # Icons
 install_data('sm.puri.Calls.png',
              install_dir : join_paths(datadir, 'icons', 'hicolor', '256x256', 'apps'))