Allow @implements of 'abstract class'

This allows a DI pattern

abstract class IFace { ... }
di.register(IFace, ...); /// <- IFace must be a class for it to have a value

class Foo implements IFace {}

Currently tsickle drops the ‘implements IFace’ because you cannot implements a class, but in the specific case of an empty abstract class we could allow it.

[evmar]

Oops, and now I overlooked your Angular 2 question. You are right that AngularJS did some crazy regex stuff. Angular2 is effectively totally different, a complete rewrite.

[evmar]

Nah I’m talking about this Angular: https://angular.io/api/core/InjectionToken , which is passing around keys.