LibGUI: Store Utf32Views in TextEditor::LineVisualData

Previously this stored the position of each visual line break, meaning
that all the text would always be painted. By storing each visual
line's Utf32View, we can skip over parts of the text, such as for code
folding.

Userland/Libraries/LibGUI/TextEditor.h

@@ -423,7 +423,7 @@ private:
     void for_each_visual_line(size_t line_index, Callback) const;
 
     struct LineVisualData {
-        Vector<size_t, 1> visual_line_breaks;
+        Vector<Utf32View> visual_lines;
         Gfx::IntRect visual_rect;
     };