LibJS: Forward receiver value to native property getters/setters

There's no reason why only (user-defined) accessors would have set the
receiver as this value for their getters/setters, this is an oversight.

Libraries/LibJS/Tests/builtins/Reflect/Reflect.get.js

@@ -60,4 +60,8 @@ describe("normal behavior", () => {
         expect(foo.getPropCalled).toBeTrue();
         expect(bar.getPropCalled).toBeTrue();
     });
+
+    test("native getter function", () => {
+        expect(Reflect.get(String.prototype, "length", "foo")).toBe(3);
+    });
 });