feat(core): properly support inheritance

## Inheritance Semantics:

Decorators:
1) list the decorators of the class and its parents in the ancestor first order
2) only use the last decorator of each kind (e.g. @Component / ...)

Constructor parameters:
If a class inherits from a parent class and does not declare
a constructor, it inherits the parent class constructor,
and with it the parameter metadata of that parent class.

Lifecycle hooks:
Follow the normal class inheritance model,
i.e. lifecycle hooks of parent classes will be called
even if the method is not overwritten in the child class.

## Example

E.g. the following is a valid use of inheritance and it will
also inherit all metadata:

```
@Directive({selector: 'someDir'})
class ParentDirective {
  constructor(someDep: SomeDep) {}

  ngOnInit() {}
}

class ChildDirective extends ParentDirective {}
```

Closes #11606
Closes #12892

modules/@angular/core/src/di/metadata.ts

@@ -6,7 +6,8 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {makeParamDecorator} from '../util/decorators';
+import {makeDecorator, makeParamDecorator} from '../util/decorators';
+
 
 /**
  * Type of the Inject decorator / constructor function.
@@ -150,7 +151,7 @@ export interface Injectable {}
  * @stable
  * @Annotation
  */
-export const Injectable: InjectableDecorator = makeParamDecorator('Injectable', []);
+export const Injectable: InjectableDecorator = <InjectableDecorator>makeDecorator('Injectable', []);
 
 /**
  * Type of the Self decorator / constructor function.