also str representation of unicode character is different.

Now that default cloudooo is updated to LibreOffice 7, this revealed some
problems with percentage values in spreadsheet cells, it was apparently
working by chance on LibreOffice 5.

This improves erp5_ods_style to use `style:style` referencing a
`number:percentage-style` through their `style:data-style-name` attribute.

Because the same thing was missing for dates to follow the input order of
datetime fields, this is also handled at the same time.

We could do something similar to support all input styles of float fields,
so that we support `1 234.5`, `1.234,5` or `1,234.5`, but this is not done
this time.

See merge request nexedi/erp5!1861