LibWeb: Move CallbackType from Bindings/ to WebIDL/

Let's stop putting generic types and AOs from the Web IDL spec into
the Bindings namespace and directory in LibWeb, and instead follow our
usual naming rules of 'directory = namespace = spec name'. The IDL
namespace is already used by LibIDL, so Web::WebIDL seems like a good
choice.

Userland/Libraries/LibWeb/WebIDL/CallbackType.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/Object.h>
+#include <LibWeb/WebIDL/CallbackType.h>
+
+namespace Web::WebIDL {
+
+CallbackType::CallbackType(JS::Object& callback, HTML::EnvironmentSettingsObject& callback_context)
+    : callback(callback)
+    , callback_context(callback_context)
+{
+}
+
+StringView CallbackType::class_name() const { return "CallbackType"sv; }
+void CallbackType::visit_edges(Cell::Visitor& visitor)
+{
+    Cell::visit_edges(visitor);
+    visitor.visit(&callback);
+}
+
+}

Userland/Libraries/LibWeb/WebIDL/CallbackType.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2021, Luke Wilde <lukew@serenityos.org>
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Heap/Cell.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::WebIDL {
+
+// https://heycam.github.io/webidl/#idl-callback-interface
+class CallbackType final : public JS::Cell {
+public:
+    CallbackType(JS::Object& callback, HTML::EnvironmentSettingsObject& callback_context);
+
+    JS::Object& callback;
+
+    // https://heycam.github.io/webidl/#dfn-callback-context
+    HTML::EnvironmentSettingsObject& callback_context;
+
+private:
+    virtual StringView class_name() const override;
+    virtual void visit_edges(Cell::Visitor&) override;
+};
+
+}