fix: add generic info for methods with thisArg of built-in classes

when enabling `noImplicitThis`, if assing this argument for
methods like `array.forEach` will cause compilation error.
This commit fixes it.

fix microsoft#12548

src/lib/es2015.core.d.ts

@@ -10,7 +10,9 @@ interface Array<T> {
       * @param thisArg If provided, it will be used as the this value for each invocation of
       * predicate. If it is not provided, undefined is used instead.
       */
-    find(predicate: (value: T, index: number, obj: Array<T>) => boolean, thisArg?: any): T | undefined;
+    find(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean): T | undefined;
+    find(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean, thisArg: undefined): T | undefined;
+    find<Z>(predicate: (this: Z, value: T, index: number, obj: Array<T>) => boolean, thisArg: Z): T | undefined;
 
     /**
       * Returns the index of the first element in the array where predicate is true, and -1
@@ -21,7 +23,9 @@ interface Array<T> {
       * @param thisArg If provided, it will be used as the this value for each invocation of
       * predicate. If it is not provided, undefined is used instead.
       */
-    findIndex(predicate: (value: T, index: number, obj: Array<T>) => boolean, thisArg?: any): number;
+    findIndex(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean): number;
+    findIndex(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean, thisArg: undefined): number;
+    findIndex<Z>(predicate: (this: Z, value: T, index: number, obj: Array<T>) => boolean, thisArg: Z): number;
 
     /**
       * Returns the this object after filling the section identified by start and end with value
@@ -52,7 +56,9 @@ interface ArrayConstructor {
       * @param mapfn A mapping function to call on every element of the array.
       * @param thisArg Value of 'this' used to invoke the mapfn.
       */
-    from<T, U>(arrayLike: ArrayLike<T>, mapfn: (v: T, k: number) => U, thisArg?: any): Array<U>;
+    from<T, U>(arrayLike: ArrayLike<T>, mapfn: (this: undefined, v: T, k: number) => U): Array<U>;
+    from<T, U>(arrayLike: ArrayLike<T>, mapfn: (this: undefined, v: T, k: number) => U, thisArg: undefined): Array<U>;
+    from<Z, T, U>(arrayLike: ArrayLike<T>, mapfn: (this: Z, v: T, k: number) => U, thisArg: Z): Array<U>;
 
 
     /**
@@ -357,7 +363,9 @@ interface ReadonlyArray<T> {
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
     */
-  find(predicate: (value: T, index: number, obj: ReadonlyArray<T>) => boolean, thisArg?: any): T | undefined;
+  find(predicate: (this: undefined, value: T, index: number, obj: ReadonlyArray<T>) => boolean): T | undefined;
+  find(predicate: (this: undefined, value: T, index: number, obj: ReadonlyArray<T>) => boolean, thisArg: undefined): T | undefined;
+  find<Z>(predicate: (this: Z, value: T, index: number, obj: ReadonlyArray<T>) => boolean, thisArg: Z): T | undefined;
 
   /**
     * Returns the index of the first element in the array where predicate is true, and -1
@@ -368,7 +376,9 @@ interface ReadonlyArray<T> {
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
     */
-  findIndex(predicate: (value: T, index: number, obj: Array<T>) => boolean, thisArg?: any): number;
+  findIndex(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean): number;
+  findIndex(predicate: (this: undefined, value: T, index: number, obj: Array<T>) => boolean, thisArg: undefined): number;
+  findIndex<Z>(predicate: (this: Z, value: T, index: number, obj: Array<T>) => boolean, thisArg: Z): number;
 }
 
 interface RegExp {