Navigate $event vars to the declaration of the $event type

[MichaelRFairhurst]

Seems like the most reasonable option given

  @Output
  EventEmitter<Foo> foo;
...
  <blah (foo)="bar($event)">

when you click on '$event'' should go to 'Foo' in the definition.

For html events (like click), we can either go to MouseEvent in ElementStream<MouseEvent> where onClick is declared, or maybe just link straight to the MouseEvent class definition.