LibWeb: Add PlatformObject class

This represents the "platform object" concept from the IDL spec, which
refers to an object that implements an IDL interface.

Userland/Libraries/LibWeb/Bindings/PlatformObject.cpp

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/PlatformObject.h>
+
+namespace Web::Bindings {
+
+PlatformObject::PlatformObject(JS::Object& prototype)
+    : JS::Object(prototype)
+{
+}
+
+PlatformObject::~PlatformObject() = default;
+
+}