Add Required<T> to lib.d.ts

src/lib/es5.d.ts

@@ -1317,6 +1317,13 @@ type Partial<T> = {
     [P in keyof T]?: T[P];
 };
 
+/**
+ * Make all properties in T required
+ */
+type Required<T> = {
+    [P in keyof T]-?: T[P];
+};
+
 /**
  * Make all properties in T readonly
  */