LibJS: Implement the object literal __proto__ property key special case

Author: https://github.com/IdanHo
Commit: 7ebb421ee9
Pull-request: https://github.com/SerenityOS/serenity/pull/12897
Issue: https://github.com/SerenityOS/serenity/issues/12896
Reviewed-by: https://github.com/davidot ✅
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Tests/object-expression-__proto__.js

@@ -0,0 +1,6 @@
+test("__proto__ property", () => {
+    expect(Object.getPrototypeOf({ __proto__: null })).toBeNull();
+    expect(Object.getPrototypeOf({ __proto__: Array.prototype })).toEqual(Array.prototype);
+    expect(Object.getPrototypeOf({ "__proto__": Array.prototype })).toEqual(Array.prototype); // prettier-ignore
+    expect(Object.getOwnPropertyNames({ __proto__: Array.prototype, test: 1 })).toEqual(["test"]);
+});