fix #12137, correct ProxyHandler signatures (#12172)

* fix #12137, correct ProxyHandler signatures

* address PR review

Author: HerringtonDarkholme

src/lib/es2015.proxy.d.ts

@@ -1,5 +1,5 @@
 interface ProxyHandler<T> {
-    getPrototypeOf? (target: T): any;
+    getPrototypeOf? (target: T): {} | null;
     setPrototypeOf? (target: T, v: any): boolean;
     isExtensible? (target: T): boolean;
     preventExtensions? (target: T): boolean;
@@ -12,11 +12,11 @@ interface ProxyHandler<T> {
     enumerate? (target: T): PropertyKey[];
     ownKeys? (target: T): PropertyKey[];
     apply? (target: T, thisArg: any, argArray?: any): any;
-    construct? (target: T, thisArg: any, argArray?: any): any;
+    construct? (target: T, argArray: any, newTarget?: any): {};
 }
 
 interface ProxyConstructor {
     revocable<T>(target: T, handler: ProxyHandler<T>): { proxy: T; revoke: () => void; };
     new <T>(target: T, handler: ProxyHandler<T>): T
 }
-declare var Proxy: ProxyConstructor;
+declare var Proxy: ProxyConstructor;