fdo#69518: Correctly handle the old constraint syntax.

We apparently support this syntax for ODF-backward compatibility.

To fix this, I resurrected ScDPObject::ParseFilters() which was removed as
unused, adjusted it for the String->OUString change, and changed the filter
data structure to the UNO one rather than using the old one we no longer use
elsewhere.

(cherry picked from commit 1d85c8df2fb9cb25fc524485339ae9f11e8da676)

Conflicts:
	sc/inc/dpobject.hxx
	sc/source/core/data/dpobject.cxx
	sc/source/core/tool/interpr2.cxx

Change-Id: If52b38aaa1e8b208fb0ef9d92a6e853decdf43e3