Shape text has two kind of spacing inside the shape's bounding box: the
shape-level margin and the paragraph-level one. Only the second was
handled in the tx algorithm so far, add support for the first.

The margins taken from constraints were way large by default: the only
explanation I found for that is that SmartArt layout sometimes
calculates in MMs, sometimes in Points, and the ratio between the two is
exactly the Impress / PowerPoint margin. So assume that indeed that unit
difference is the reason for the smaller in-PowerPoint margin values and
do the same on our side.

Change-Id: I6f1e54301e2e9b33a7e721be34244d968cccf42d
Reviewed-on: https://gerrit.libreoffice.org/68453Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins