meson: Improve and validate desktop entry

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

data/sm.puri.Calls.desktop

@@ -1,13 +1,14 @@
 [Desktop Entry]
 Name=Calls
 GenericName=Phone
-Comment=Make telephone calls
+Comment=A phone dialer and call handler
 # Translators: These are desktop search terms. Do not translate semicolons, end line with a semicolon.
 Keywords=Telephone;Call;Phone;Dial;Dialer;PTSN;
 # Translators: Do NOT translate or transliterate this text (this is an icon file name)!
 Icon=sm.puri.Calls
 TryExec=calls
-Exec=calls
+Exec=calls %U
 Type=Application
+StartupNotify=true
 Terminal=false
 Categories=GNOME;GTK;Telephony;