fdo#63786 rhbz#1081968: fix PDF export of cropped SVG

When a META_FLOATTRANSPARENT_ACTION is exported, the
beginTransparencyGroup()/endTransparencyGroup() will write something
like "Q 0 0 0 rg" where the Q clears the previously set clipping region,
which is then not restored.

bdf75c7d9bce985ed10a9c41d03420f33ce82142 appears to be a fix for a
previous related problem; this essentially reverts it since it
introduced the current cropping problem.  (Particularly funny is the
comment "force reemitting clip region" since the commit does the
opposite.)

It does not really make sense to me to write something to the page
content stream from beginRedirect()/endRedirect(), because that does not
actually have any effect on the _content_ of the substream, because the
referencing of the substream is only written _after_ endRedirect()
returns, so basically what is written can in the best case cancel itself
out and in the worst case introduce bugs; the state manipulations there
are just to modify the m_aCurrentPDFState following the push()/pop() (it
is necessary to clear the clip region before starting the substream to
avoid spurious "Q" at the beginning of the stream).

Change-Id: I4a5f57b784068bd7d3ba187115444574f7418195
(cherry picked from commit e8062623355fcf3e65beae7f8f5e4d46384141f2)
Reviewed-on: https://gerrit.libreoffice.org/8813
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>