chore: improve angular2.d.ts file

- support ambient and import format for .d.ts

modules/angular2/src/util/decorators.ts

@@ -6,11 +6,13 @@ export interface ClassDefinition {
 }
 
 export interface TypeDecorator {
-  (cls: any): any;
+  <T>(cls: T): T;
   annotations: Array<any>;
   Class(obj: ClassDefinition): Type;
 }
 
+export interface ParamaterDecorator { (cls: Type, unusedKey: any, index: number): void }
+
 function extractAnnotation(annotation: any): any {
   if (isFunction(annotation) && annotation.hasOwnProperty('annotation')) {
     // it is a decorator, extract annotation