LibWebView: Implement a WebView-based Inspector client

This is modeled after a similar implementation for the JS console.

This client takes over an inspector WebView (created by the chrome) to
create the inspector application. Currently, this application includes
the DOM tree and accessibility tree as a first pass. It can later be
extended to included the style tables, the JS console itself, etc.

Userland/Libraries/LibWebView/InspectorClient.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Function.h>
+#include <AK/JsonValue.h>
+#include <AK/StringView.h>
+#include <LibWebView/ViewImplementation.h>
+
+#pragma once
+
+namespace WebView {
+
+class InspectorClient {
+public:
+    InspectorClient(ViewImplementation& content_web_view, ViewImplementation& inspector_web_view);
+    ~InspectorClient();
+
+    void inspect();
+    void reset();
+
+    void select_hovered_node();
+    void select_default_node();
+    void clear_selection();
+
+    Function<void(ErrorOr<ViewImplementation::DOMNodeProperties>)> on_dom_node_properties_received;
+
+private:
+    void maybe_load_inspector();
+    void generate_dom_tree(StringBuilder&);
+    void generate_accessibility_tree(StringBuilder&);
+
+    void select_node(i32 node_id);
+
+    ViewImplementation& m_content_web_view;
+    ViewImplementation& m_inspector_web_view;
+
+    Optional<JsonValue> m_dom_tree;
+    Optional<JsonValue> m_accessibility_tree;
+
+    Optional<i32> m_body_node_id;
+    Optional<i32> m_pending_selection;
+
+    bool m_inspector_loaded { false };
+};
+
+}