feat($compile): allow required controllers to be bound to the directive controller

If directives are required through an object hash, rather than a string or array,
the required directives' controllers are bound to the current directive's controller
in much the same way as the properties are bound to using `bindToController`.

The binding is done after the controller has been constructed and all the bindings
are guaranteed to be complete by the time the controller's `$onInit` method
is called.

This change makes it much simpler to access require controllers without the
need for manually wiring them up in link functions. In particular this
enables support for `require` in directives defined using `mod.component()`

Author: petebacondarwin

test/ng/compileSpec.js

@@ -9579,5 +9579,5 @@ describe('$compile', function() {
         }));
       });
     });
-   });
+  });
 });