LibWeb: Implement ModuleMap and expose it on EnvironmentSettingsObject

This patch adds the ModuleMap class used to keep track of the type and
url of a module as well as the fetching state associated. Each
environment settings object now also has a module map.

Userland/Libraries/LibWeb/HTML/Scripting/ModuleMap.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2022, networkException <networkexception@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/Scripting/ModuleMap.h>
+
+namespace Web::HTML {
+
+bool ModuleMap::is_fetching(AK::URL const& url, String const& type) const
+{
+    return is(url, type, EntryType::Fetching);
+}
+
+bool ModuleMap::is_failed(AK::URL const& url, String const& type) const
+{
+    return is(url, type, EntryType::Failed);
+}
+
+bool ModuleMap::is(AK::URL const& url, String const& type, EntryType entry_type) const
+{
+    auto value = m_values.get({ url, type });
+    if (!value.has_value())
+        return false;
+
+    return value->type == entry_type;
+}
+
+Optional<ModuleMap::Entry> ModuleMap::get(AK::URL const& url, String const& type) const
+{
+    return m_values.get({ url, type });
+}
+
+AK::HashSetResult ModuleMap::set(AK::URL const& url, String const& type, Entry entry)
+{
+    auto callbacks = m_callbacks.get({ url, type });
+    if (callbacks.has_value())
+        for (auto const& callback : *callbacks)
+            callback(entry);
+
+    return m_values.set({ url, type }, entry);
+}
+
+void ModuleMap::wait_for_change(AK::URL const& url, String const& type, Function<void(Entry)> callback)
+{
+    m_callbacks.ensure({ url, type }).append(move(callback));
+}
+
+}