tdf#121845 rework custom shape path command U and T

Hi all,

I have submitted https://gerrit.libreoffice.org/68029 for discussion.

It has no unit tests yet. I would like your opinion on the changes 
before putting time into unit tests.

Critical parts are
(1) My opinion, how the commands U and T should work, see comments in 
https://bugs.documentfoundation.org/show_bug.cgi?id=121845.
The description in the ODF 1.2 spec seems to be a copy of the VML spec 
proposal and is not clear. The implementation in MS Office is surely 
wrong, because it sets 0 degree in up-direction. Scribus has copied from 
Calligra. I have got no answer from Calligra, why they do it that way. 
The main problem in current implementation in LO is, that handles use 
the angle in different orientation than command U.

(2) I have made the case distinction on the draw:type attribute.
I'm not sure, that this is the correct way to go. A different way would 
be to add an internal property to shapes, which filter was used on 
opening. However that would touch much more parts and might be beyond my 
skills.

Other comments on the proposal are welcomed too.

Kind regards
Regina