LibWeb: Make DOM inspector overlay rects a little nicer

Instead of just the outline, fill them with some semi-transparent color.
Also add tag name, ID, classes and coordinates to the little tooltip.
Finally, use the border box instead of the context box for metrics,
same as other browsers.

Userland/Libraries/LibWeb/DOM/Node.h

@@ -208,6 +208,8 @@ public:
 
     bool is_uninteresting_whitespace_node() const;
 
+    String debug_description() const;
+
 protected:
     Node(Document&, NodeType);