Improve types of 'instantiate' and 'invoke' of IInjectorService.

The result is inferred form the argument, which removes the need of any cast.

types/angular/angular-tests.ts

@@ -470,6 +470,22 @@ namespace TestInjector {
 
     $injector.annotate(() => {});
     $injector.annotate(() => {}, true);
+
+    // $injector.instantiate
+    {
+        class Foobar {
+            constructor($q) {}
+        }
+        let result: Foobar = $injector.instantiate(Foobar);
+    }
+
+    // $injector.invoke
+    {
+        function foobar(v: boolean): number {
+            return 7;
+        }
+        let result: number = $injector.invoke(foobar);
+    }
 }
 
 // Promise signature tests

types/angular/index.d.ts

@@ -1978,9 +1978,9 @@ declare namespace angular {
             get(name: '$window'): IWindowService;
             get<T>(name: '$xhrFactory'): IXhrFactory<T>;
             has(name: string): boolean;
-            instantiate<T>(typeConstructor: Function, locals?: any): T;
+            instantiate<T>(typeConstructor: {new(...args: any[]): T}, locals?: any): T;
             invoke(inlineAnnotatedFunction: any[]): any;
-            invoke(func: Function, context?: any, locals?: any): any;
+            invoke<T>(func: (...args: any[]) => T, context?: any, locals?: any): T;
             strictDi: boolean;
         }