Ladybird: Allow right clicking and inspecting elements

This adds "Inspect Element" (currently the only entry) to the context
menu for the page, which will do what you expect (most of the time),
and bring up the Inspector with hovered element selected.

Ladybird/InspectorWidget.h

@@ -30,6 +30,13 @@ public:
         bool operator==(Selection const& other) const = default;
     };
 
+    bool dom_loaded() const { return m_dom_loaded; }
+
+    void set_selection(Selection);
+    void clear_selection();
+
+    void select_default_node();
+
     void clear_dom_json();
     void set_dom_json(StringView dom_json);
 
@@ -52,6 +59,11 @@ private:
     ModelTranslator m_computed_style_model {};
     ModelTranslator m_resolved_style_model {};
     ModelTranslator m_custom_properties_model {};
+
+    QTreeView* m_dom_tree_view { nullptr };
+
+    bool m_dom_loaded { false };
+    Optional<Selection> m_pending_selection {};
 };
 
 }