LibWeb: Begin implementing SharedWorker

Shared workers are essentially just workers that may be accessed from
scripts within the same origin. There are plenty of FIXMEs here (mostly
building on existing worker FIXMEs that are already in place), but this
lets us run the shared worker variants of WPT tests.

Libraries/LibWeb/HTML/SharedWorkerGlobalScope.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/SharedWorkerExposedInterfaces.h>
+#include <LibWeb/HTML/SharedWorkerGlobalScope.h>
+#include <LibWeb/Page/Page.h>
+
+namespace Web::HTML {
+
+GC_DEFINE_ALLOCATOR(SharedWorkerGlobalScope);
+
+HashTable<GC::RawRef<SharedWorkerGlobalScope>>& all_shared_worker_global_scopes()
+{
+    static HashTable<GC::RawRef<SharedWorkerGlobalScope>> set;
+    return set;
+}
+
+SharedWorkerGlobalScope::SharedWorkerGlobalScope(JS::Realm& realm, GC::Ref<Web::Page> page, String name)
+    : WorkerGlobalScope(realm, page)
+    , m_name(move(name))
+{
+    all_shared_worker_global_scopes().set(*this);
+}
+
+SharedWorkerGlobalScope::~SharedWorkerGlobalScope() = default;
+
+void SharedWorkerGlobalScope::initialize_web_interfaces_impl()
+{
+    auto& realm = this->realm();
+
+    Bindings::add_shared_worker_exposed_interfaces(*this);
+
+    SharedWorkerGlobalScopeGlobalMixin::initialize(realm, *this);
+    Base::initialize_web_interfaces_impl();
+}
+
+void SharedWorkerGlobalScope::finalize()
+{
+    Base::finalize();
+    WindowOrWorkerGlobalScopeMixin::finalize();
+
+    all_shared_worker_global_scopes().remove(*this);
+}
+
+// https://html.spec.whatwg.org/multipage/workers.html#dom-sharedworkerglobalscope-close
+void SharedWorkerGlobalScope::close()
+{
+    // The close() method steps are to close a worker given this.
+    close_a_worker();
+}
+
+#define __ENUMERATE(attribute_name, event_name)                                     \
+    void SharedWorkerGlobalScope::set_##attribute_name(WebIDL::CallbackType* value) \
+    {                                                                               \
+        set_event_handler_attribute(event_name, move(value));                       \
+    }                                                                               \
+                                                                                    \
+    WebIDL::CallbackType* SharedWorkerGlobalScope::attribute_name()                 \
+    {                                                                               \
+        return event_handler_attribute(event_name);                                 \
+    }
+ENUMERATE_SHARED_WORKER_GLOBAL_SCOPE_EVENT_HANDLERS(__ENUMERATE)
+#undef __ENUMERATE
+
+}