Better typings for Promise executor, like microsoft#31117

Author: jablko

src/lib/es2015.promise.d.ts

@@ -10,7 +10,7 @@ interface PromiseConstructor {
      * a resolve callback used to resolve the promise with a value or the result of another promise,
      * and a reject callback used to reject the promise with a provided reason or error.
      */
-    new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>;
+    new <T>(executor: (resolve: (value?: T) => void, reject: (reason?: any) => void) => void): Promise<T extends PromiseLike<infer U> ? U : T>;
 
     /**
      * Creates a Promise that is resolved with an array of results when all of the provided Promises