LibWeb: Add the TextEncoder interface

This is from the Encoding Standard (https://encoding.spec.whatwg.org),
and therefore gets its own namespace and subdirectory within LibWeb :^)

Userland/Libraries/LibWeb/Encoding/TextEncoder.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <LibJS/Forward.h>
+#include <LibWeb/Bindings/Wrappable.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::Encoding {
+
+// https://encoding.spec.whatwg.org/#textencoder
+class TextEncoder
+    : public RefCounted<TextEncoder>
+    , public Bindings::Wrappable {
+public:
+    using WrapperType = Bindings::TextEncoderWrapper;
+
+    static NonnullRefPtr<TextEncoder> create()
+    {
+        return adopt_ref(*new TextEncoder());
+    }
+
+    static NonnullRefPtr<TextEncoder> create_with_global_object(Bindings::WindowObject&)
+    {
+        return TextEncoder::create();
+    }
+
+protected:
+    // https://encoding.spec.whatwg.org/#dom-textencoder
+    TextEncoder() = default;
+};
+
+}