Restructure public side of input_events service.

sky/tests/services/event-sender.sky

 <sky>
 <import src="../resources/chai.sky" />
 <import src="../resources/mocha.sky" />
-<import src="/mojo/services/public/interfaces/input_events/input_event_constants.mojom.sky" as="constants" />
-<import src="/mojo/services/public/interfaces/input_events/input_events.mojom.sky" as="events" />
+<import src="/mojo/services/input_events/public/interfaces/input_event_constants.mojom.sky" as="constants" />
+<import src="/mojo/services/input_events/public/interfaces/input_events.mojom.sky" as="events" />
 <import src="/sky/framework/shell.sky" as="shell" />
 <import src="/sky/services/testing/test_harness.mojom.sky" as="harness" />
 
 <script>
 describe('Sky event sender', function() {
   it('should be able to send events', function(done) {
     var sky = document.querySelector('sky')
     sky.focus();
     sky.addEventListener('keypress', function(event) {
       assert.equal(event.type, 'keypress');
@@ skipping 10 matching lines @@
         text: 0x41,
         unmodified_text: 0x41,
         is_char: true,
         character: 0x41,
       }),
     }));
   });
 });
 </script>
 </sky>