Recently xmloff started to use XML_DATASOURCE for "form:datasource"
but it actually means "data-source".
Add XML_DATA_SOURCE and use it for "db:data-source".
(regression from 3de38e9556)
Change-Id: I893efd3fb0fb7c19ae998442459bf36cb1da0b20
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/109019
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>
