Spreadsheet alter

I have developed this feature, please review it.

The last submitted patch, 2: xls_serialization-spreadsheet_alter-3339290-2.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

Fixed the code indent

The last submitted patch, 4: xls_serialization-spreadsheet_alter-3339290-3.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

That would definitely be something interesting to have.

Would you mind opening an MR for it?