LibJS: Disable optimization in IteratorNextUnpack if next() is redefined

81b6a11 regressed correctness by always bypassing the `next()` method
resolution for built-in iterators, causing incorrect behavior when
`next()` was redefined on built-in prototypes. This change fixes the
issue by storing a flag on built-in prototypes indicating whether
`next()` has ever been redefined.

Libraries/LibJS/Tests/redefine-next-in-builtin-iterators.js

@@ -0,0 +1,46 @@
+describe("redefine next() in built in iterators", () => {
+    test("redefine next() in ArrayIteratorPrototype", () => {
+        let arrayIteratorPrototype = Object.getPrototypeOf([].values());
+        let originalNext = arrayIteratorPrototype.next;
+        let counter = 0;
+        arrayIteratorPrototype.next = function () {
+            counter++;
+            return originalNext.apply(this, arguments);
+        };
+        for (let i of [1, 2, 3]) {
+        }
+        expect(counter).toBe(4);
+    });
+
+    test("redefine next() in MapIteratorPrototype", () => {
+        let m = new Map([
+            [1, 1],
+            [2, 2],
+            [3, 3],
+        ]);
+        let mapIteratorPrototype = Object.getPrototypeOf(m.values());
+        let originalNext = mapIteratorPrototype.next;
+        let counter = 0;
+        mapIteratorPrototype.next = function () {
+            counter++;
+            return originalNext.apply(this, arguments);
+        };
+        for (let v of m.values()) {
+        }
+        expect(counter).toBe(4);
+    });
+
+    test("redefine next() in SetIteratorPrototype", () => {
+        let s = new Set([1, 2, 3]);
+        let setIteratorPrototype = Object.getPrototypeOf(s.values());
+        let originalNext = setIteratorPrototype.next;
+        let counter = 0;
+        setIteratorPrototype.next = function () {
+            counter++;
+            return originalNext.apply(this, arguments);
+        };
+        for (let v of s.values()) {
+        }
+        expect(counter).toBe(4);
+    });
+});