LibWeb: Move HistoryHandlingBehavior enum to its own header

This avoids a header cycle in a subsequent patch.

Userland/Libraries/LibWeb/HTML/HistoryHandlingBehavior.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::HTML {
+
+// https://html.spec.whatwg.org/multipage/browsing-the-web.html#history-handling-behavior
+enum class HistoryHandlingBehavior {
+    Default,
+    EntryUpdate,
+    Reload,
+    Replace,
+};
+
+}