LibJS: Stub out Atomics.notify

We don't have the facilities to implement this method fully (namely, a
fully realized SharedArrayBuffer). But we can implement enough to
validate the values passed in by the user.

Userland/Libraries/LibJS/Tests/builtins/Atomics/Atomics.notify.js

@@ -0,0 +1,56 @@
+describe("errors", () => {
+    test("called on non-TypedArray", () => {
+        expect(() => {
+            Atomics.notify(Symbol.hasInstance, 0, 0);
+        }).toThrowWithMessage(TypeError, "Not an object of type TypedArray");
+    });
+
+    test("detached buffer", () => {
+        expect(() => {
+            const typedArray = new Int32Array(4);
+            detachArrayBuffer(typedArray.buffer);
+
+            Atomics.notify(typedArray, 0, 0);
+        }).toThrowWithMessage(TypeError, "ArrayBuffer is detached");
+    });
+
+    test("invalid TypedArray type", () => {
+        expect(() => {
+            const typedArray = new Float32Array(4);
+            Atomics.notify(typedArray, 0, 0);
+        }).toThrowWithMessage(
+            TypeError,
+            "Typed array Float32Array element type is not Int32 or BigInt64"
+        );
+    });
+
+    test("invalid index", () => {
+        expect(() => {
+            const buffer = new SharedArrayBuffer(4 * Int32Array.BYTES_PER_ELEMENT);
+            const typedArray = new Int32Array(buffer);
+
+            Atomics.notify(typedArray, 4, 0);
+        }).toThrowWithMessage(RangeError, "Index 4 is out of range of array length 4");
+    });
+
+    test("invalid count", () => {
+        expect(() => {
+            const buffer = new SharedArrayBuffer(4 * Int32Array.BYTES_PER_ELEMENT);
+            const typedArray = new Int32Array(buffer);
+
+            Atomics.notify(typedArray, 0, Symbol.hasInstance);
+        }).toThrowWithMessage(TypeError, "Cannot convert symbol to number");
+    });
+});
+
+test("basic functionality", () => {
+    test("invariants", () => {
+        expect(Atomics.notify).toHaveLength(3);
+    });
+
+    test("non-shared ArrayBuffer", () => {
+        const typedArray = new Int32Array(4);
+        const waiters = Atomics.notify(typedArray, 0, 0);
+        expect(waiters).toBe(0);
+    });
+});