Fix tpromise callback sig for ts 2.4 (#30228)

Fixes #30216

Changes the TPromise callback interface as suggested by https://github.com/Microsoft/vscode/issues/30216#issuecomment-313558951 to fix async functions when compiling using ts 2.4+

src/vs/base/common/winjs.base.d.ts

@@ -47,7 +47,7 @@ export declare class Promise {
  * The value callback to complete a promise
  */
 export interface TValueCallback<T> {
-	(value: T): void;
+	(value: T | Thenable<T>): void;
 }
 
 

src/vs/monaco.d.ts

@@ -47,7 +47,7 @@ declare module monaco {
 	 * The value callback to complete a promise
 	 */
 	export interface TValueCallback<T> {
-		(value: T): void;
+		(value: T | Thenable<T>): void;
 	}