Improve csv export

- Wrap cell content in " [...] " in order to keep line breaks and other special chars 
- Replace any " with "" as " needs to be escaped in csv

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -5995,8 +5995,9 @@ namespace Avalonia.Controls
             var numberOfItem = clipboardRowContent.Count;
             for (int cellIndex = 0; cellIndex < numberOfItem; cellIndex++)
             {
-                var cellContent = clipboardRowContent[cellIndex];
+                var cellContent = clipboardRowContent[cellIndex].Content?.ToString();
-                text.Append(cellContent.Content);
+                cellContent = cellContent?.Replace("\"", "\"\"");
+                text.Append($"\"{cellContent}\"");
                 if (cellIndex < numberOfItem - 1)
                 {
                     text.Append('\t');