The problem is that when loading from a stream, there is no BaseURL and
also no storage for the document.

Due to the lack of BaseURL, the sfx2::createBaseURI() throws and loading
RDF metadata fails, which also pops up an annoying warning dialog.

Try to handle this in a similar way than a newly created document (see
GetDMA()), by using the vnd.sun.star.tdoc scheme URL for the document;
this however currently requires that the document has a XStorage, which
is also not the case here.

So add another UNO method to tdoc UCP's tdoc_ucp::ContentProvider,
to split out the creation of the tdoc schema URL from the creation of
the ucb Content, to get rid of the XStorage requirement.

Change-Id: Ica62743f9d21db0b1464b70db1a62ebc61989ef8
Reviewed-on: https://gerrit.libreoffice.org/67882
Tested-by: Jenkins
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>