LibJS: Add a basic unit test for the "with" statement

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/1fad95fec5d

Libraries/LibJS/Tests/with-basic.js

@@ -0,0 +1,20 @@
+test("basic with statement functionality", () => {
+    var object = { "foo": 5, "bar": 6, "baz": 7 };
+    var qux = 1;
+
+    var bar = 99;
+
+    with (object) {
+        expect(foo).toBe(5);
+        expect(bar).toBe(6);
+        expect(baz).toBe(7);
+        expect(qux).toBe(1);
+        expect(typeof quz).toBe("undefined");
+
+        bar = 2;
+    }
+
+    expect(object.bar).toBe(2);
+
+    expect(bar).toBe(99);
+});