In DOCX, w:pos specifies the position of the current custom tab stop
with respect to the current page margins.
But in ODT, zero position could be page margins or paragraph indent
according to used settings DocumentSettingId::TABS_RELATIVE_TO_INDENT

Added new unit test.

Change-Id: Ic56a8527380b6562f4239df1edce0c9b4649af24
Reviewed-on: https://gerrit.libreoffice.org/63460
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>