LibDevTools: Support highlighting DOM nodes hovered in the inspector

Author: https://github.com/trflynn89
Commit: 6e8d77ff7f
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3666
Reviewed-by: https://github.com/AtkinsSJ

Libraries/LibDevTools/Actors/WalkerActor.h

@@ -11,6 +11,8 @@
 #include <AK/NonnullRefPtr.h>
 #include <AK/Optional.h>
 #include <LibDevTools/Actor.h>
+#include <LibWeb/CSS/Selector.h>
+#include <LibWeb/Forward.h>
 
 namespace DevTools {
 
@@ -26,6 +28,13 @@ public:
     static bool is_suitable_for_dom_inspection(JsonValue const&);
     JsonValue serialize_root() const;
 
+    struct DOMNode {
+        JsonObject const& node;
+        Web::UniqueNodeID id { 0 };
+        Optional<Web::CSS::Selector::PseudoElement::Type> pseudo_element;
+    };
+    Optional<DOMNode> dom_node(StringView actor);
+
 private:
     WalkerActor(DevToolsServer&, String name, WeakPtr<TabActor>, JsonObject dom_tree);