Add link titles for all links in the class reference

This makes them display in a nicer way in the editor help.
(The title will display instead of the full URL.)

doc/classes/InputEventMouseButton.xml

@@ -7,7 +7,7 @@
 		Contains mouse click information. See [method Node._input].
 	</description>
 	<tutorials>
-		<link>https://docs.godotengine.org/en/latest/tutorials/inputs/mouse_and_input_coordinates.html</link>
+		<link title="Mouse and input coordinates">https://docs.godotengine.org/en/latest/tutorials/inputs/mouse_and_input_coordinates.html</link>
 	</tutorials>
 	<methods>
 	</methods>