refactor(core): simplify decorators

Every decorator now is made of the following:
- a function that can be used
as a decorator or as a constructor. This function
also can be used for `instanceof` checks.
- a type for this function (callable and newable)
- a type that describes the shape of the data
  that the user needs to pass to the decorator
  as well as the instance of the metadata

The docs for decorators live at the followig places
so that IDEs can discover them correctly:
- General description of the decorator is placed on the
  `...Decorator` interface on the callable function
  definition
- Property descriptions are placed on the interface
  that describes the metadata produces by the decorator

modules/@angular/core/test/reflection/reflector_common.ts

@@ -8,33 +8,33 @@
 
 import {makeDecorator, makeParamDecorator, makePropDecorator} from '@angular/core/src/util/decorators';
 
-export class ClassDecoratorMeta {
-  constructor(public value: any /** TODO #9100 */) {}
+export interface ClassDecoratorFactory {
+  (data: ClassDecorator): any;
+  new (data: ClassDecorator): ClassDecorator;
 }
 
-export class ParamDecoratorMeta {
-  constructor(public value: any /** TODO #9100 */) {}
-}
+export interface ClassDecorator { value: any; }
 
-export class PropDecoratorMeta {
-  constructor(public value: any /** TODO #9100 */) {}
-}
+export interface ParamDecorator { value: any; }
+
+export interface PropDecorator { value: any; }
 
 export function classDecorator(value: any /** TODO #9100 */) {
-  return new ClassDecoratorMeta(value);
+  return new ClassDecorator({value: value});
 }
 
 export function paramDecorator(value: any /** TODO #9100 */) {
-  return new ParamDecoratorMeta(value);
+  return new ParamDecorator(value);
 }
 
 export function propDecorator(value: any /** TODO #9100 */) {
-  return new PropDecoratorMeta(value);
+  return new PropDecorator(value);
 }
 
-/** @Annotation */ export var ClassDecorator = makeDecorator(ClassDecoratorMeta);
-/** @Annotation */ export var ParamDecorator = makeParamDecorator(ParamDecoratorMeta);
-/** @Annotation */ export var PropDecorator = makePropDecorator(PropDecoratorMeta);
+/** @Annotation */ export const ClassDecorator =
+    <ClassDecoratorFactory>makeDecorator({value: undefined});
+/** @Annotation */ export const ParamDecorator = makeParamDecorator([['value', undefined]]);
+/** @Annotation */ export const PropDecorator = makePropDecorator([['value', undefined]]);
 
 // used only in Dart
 export class HasGetterAndSetterDecorators {}

modules/@angular/core/test/reflection/reflector_spec.ts

@@ -20,7 +20,7 @@ class AType {
   constructor(value: any /** TODO #9100 */) { this.value = value; }
 }
 
-@ClassDecorator('class')
+@ClassDecorator({value: 'class'})
 class ClassWithDecorators {
   @PropDecorator('p1') @PropDecorator('p2') a: any /** TODO #9100 */;
   b: any /** TODO #9100 */;