SIGDIGITS rounds a value to a determined number of significant digits.

Change-Id: I5dbfb638bf17ca109f9a14b3588d6d6c103edfa4
Reviewed-on: https://gerrit.libreoffice.org/34148Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>