LibHTML: Use LayoutText::text_for_rendering() in layout tree dumps

This way the fragment offsets make a lot more sense, since they assume
whitespace has already been collapsed.

Libraries/LibHTML/Dump.cpp

@@ -119,8 +119,8 @@ void dump_tree(const LayoutNode& layout_node)
                     for (int i = 0; i < indent; ++i)
                         dbgprintf("    ");
                     auto& layout_text = static_cast<const LayoutText&>(fragment.layout_node());
-                    dbgprintf("        text: \"%s\"\n",
-                        String(Utf8View(layout_text.node().data()).substring_view(fragment.start(), fragment.length()).as_string()).characters());
+                    auto fragment_text = layout_text.text_for_rendering().substring(fragment.start(), fragment.length());
+                    dbgprintf("        text: \"%s\"\n", fragment_text.characters());
                 }
             }
         }

Libraries/LibHTML/Layout/LayoutText.h

@@ -13,6 +13,7 @@ public:
     const Text& node() const { return static_cast<const Text&>(*LayoutNode::node()); }
 
     const String& text_for_style(const StyleProperties&) const;
+    const String& text_for_rendering() const { return m_text_for_rendering; }
 
     virtual const char* class_name() const override { return "LayoutText"; }
     virtual bool is_text() const final { return true; }