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/util/decorators.ts

@@ -262,7 +262,7 @@ export function makeDecorator(
   const metaCtor = makeMetadataCtor([props]);
 
   function DecoratorFactory(objOrType: any): (cls: any) => any {
-    if (!(Reflect && Reflect.getMetadata)) {
+    if (!(Reflect && Reflect.getOwnMetadata)) {
       throw 'reflect-metadata shim is required when using class decorators';
     }
 
@@ -327,7 +327,7 @@ export function makeParamDecorator(
     return ParamDecorator;
 
     function ParamDecorator(cls: any, unusedKey: any, index: number): any {
-      const parameters: any[][] = Reflect.getMetadata('parameters', cls) || [];
+      const parameters: any[][] = Reflect.getOwnMetadata('parameters', cls) || [];
 
       // there might be gaps if some in between parameters do not have annotations.
       // we pad with nulls.