LibWeb: Extract the (un)focus steps out of HTMLElement

The (un)focus steps have no dependency on HTMLElement, thus we can
extract them into their own file. This allows them to be called
anywhere.

Userland/Libraries/LibWeb/HTML/Focus.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Optional.h>
+#include <AK/String.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::HTML {
+
+void run_focusing_steps(DOM::Node* new_focus_target, DOM::Node* fallback_target = nullptr, Optional<String> focus_trigger = {});
+void run_unfocusing_steps(DOM::Node* old_focus_target);
+
+}