LibWeb: Hide uninteresting whitespace text nodes from DOM inspector

Use a simple heuristic to exclude uninteresting whitespace and
de-clutter the inspector's DOM tree.

Uninteresting whitespace is currently one of these:
- Non-rendered whitespace-only text nodes
- Rendered whitespace-only text nodes between block-level elements

Userland/Libraries/LibWeb/DOM/Node.h

@@ -202,6 +202,8 @@ public:
 
     NonnullRefPtr<Node> get_root_node(GetRootNodeOptions const& options = {});
 
+    bool is_uninteresting_whitespace_node() const;
+
 protected:
     Node(Document&, NodeType);