meson: Improve and validate desktop entry

This improves the desktop entry a bit and adds a test to validate it.

data/meson.build

@@ -1,7 +1,16 @@
 datadir = get_option('datadir')
 
+# Desktop file
 install_data('sm.puri.Calls.desktop',
              install_dir : join_paths(datadir, 'applications'))
 
+desktop_utils = find_program('desktop-file-validate', required: false)
+if desktop_utils.found()
+    test('Validate desktop file', desktop_utils,
+        args: ['sm.puri.Calls.desktop']
+    )
+endif
+
+# Icons
 install_data('sm.puri.Calls.png',
              install_dir : join_paths(datadir, 'icons', 'hicolor', '256x256', 'apps'))