LibWeb: Introduce CustomElementRegistry and creating custom elements

The main missing feature here is form associated custom elements.

Userland/Libraries/LibWeb/HTML/CustomElements/CustomElementDefinition.h

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2023, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <LibWeb/HTML/HTMLElement.h>
+#include <LibWeb/WebIDL/CallbackType.h>
+
+namespace Web::HTML {
+
+struct AlreadyConstructedCustomElementMarker {
+};
+
+// https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element-definition
+class CustomElementDefinition : public JS::Cell {
+    JS_CELL(CustomElementDefinition, JS::Cell);
+
+    using LifecycleCallbacksStorage = OrderedHashMap<FlyString, JS::Handle<WebIDL::CallbackType>>;
+    using ConstructionStackStorage = Vector<Variant<JS::Handle<DOM::Element>, AlreadyConstructedCustomElementMarker>>;
+
+    static JS::NonnullGCPtr<CustomElementDefinition> create(JS::Realm& realm, String const& name, String const& local_name, WebIDL::CallbackType& constructor, Vector<String>&& observed_attributes, LifecycleCallbacksStorage&& lifecycle_callbacks, bool form_associated, bool disable_internals, bool disable_shadow)
+    {
+        return realm.heap().allocate<CustomElementDefinition>(realm, name, local_name, constructor, move(observed_attributes), move(lifecycle_callbacks), form_associated, disable_internals, disable_shadow).release_allocated_value_but_fixme_should_propagate_errors();
+    }
+
+    ~CustomElementDefinition() = default;
+
+    String const& name() const { return m_name; }
+    String const& local_name() const { return m_local_name; }
+
+    WebIDL::CallbackType& constructor() { return *m_constructor; }
+    WebIDL::CallbackType const& constructor() const { return *m_constructor; }
+
+    Vector<String> const& observed_attributes() const { return m_observed_attributes; }
+
+    LifecycleCallbacksStorage const& lifecycle_callbacks() const { return m_lifecycle_callbacks; }
+
+    ConstructionStackStorage& construction_stack() { return m_construction_stack; }
+    ConstructionStackStorage const& construction_stack() const { return m_construction_stack; }
+
+    bool form_associated() const { return m_form_associated; }
+    bool disable_internals() const { return m_disable_internals; }
+    bool disable_shadow() const { return m_disable_shadow; }
+
+private:
+    CustomElementDefinition(String const& name, String const& local_name, WebIDL::CallbackType& constructor, Vector<String>&& observed_attributes, LifecycleCallbacksStorage&& lifecycle_callbacks, bool form_associated, bool disable_internals, bool disable_shadow)
+        : m_name(name)
+        , m_local_name(local_name)
+        , m_constructor(JS::make_handle(constructor))
+        , m_observed_attributes(move(observed_attributes))
+        , m_lifecycle_callbacks(move(lifecycle_callbacks))
+        , m_form_associated(form_associated)
+        , m_disable_internals(disable_internals)
+        , m_disable_shadow(disable_shadow)
+    {
+    }
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-name
+    // A name
+    //     A valid custom element name
+    String m_name;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-local-name
+    // A local name
+    //     A local name
+    String m_local_name;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-constructor
+    // A Web IDL CustomElementConstructor callback function type value wrapping the custom element constructor
+    JS::Handle<WebIDL::CallbackType> m_constructor;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-observed-attributes
+    // A list of observed attributes
+    //     A sequence<DOMString>
+    Vector<String> m_observed_attributes;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-lifecycle-callbacks
+    // A collection of lifecycle callbacks
+    //     A map, whose keys are the strings "connectedCallback", "disconnectedCallback", "adoptedCallback", "attributeChangedCallback",
+    //     "formAssociatedCallback", "formDisabledCallback", "formResetCallback", and "formStateRestoreCallback".
+    //     The corresponding values are either a Web IDL Function callback function type value, or null.
+    //     By default the value of each entry is null.
+    LifecycleCallbacksStorage m_lifecycle_callbacks;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-construction-stack
+    // A construction stack
+    //     A list, initially empty, that is manipulated by the upgrade an element algorithm and the HTML element constructors.
+    //     Each entry in the list will be either an element or an already constructed marker.
+    ConstructionStackStorage m_construction_stack;
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-form-associated
+    // A form-associated boolean
+    //     If this is true, user agent treats elements associated to this custom element definition as form-associated custom elements.
+    bool m_form_associated { false };
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-disable-internals
+    // A disable internals boolean
+    //     Controls attachInternals().
+    bool m_disable_internals { false };
+
+    // https://html.spec.whatwg.org/multipage/custom-elements.html#concept-custom-element-definition-disable-shadow
+    // A disable shadow boolean
+    //     Controls attachShadow().
+    bool m_disable_shadow { false };
+};
+
+}