writerfilter: salvage a field parameter parsing train wreck

Field parameters get horribly maimed by lcl_ExtractParameter which
clearly has never worked in its 7 years of existence (and looking at the
inanity at the call sites makes one wonder what the author was smoking).

The format is actually quite annoying, since spaces between parameters
are optional.

The old RTF filter was at least able to parse "PAGEREF bookmark" fields,
so this fixes such regressions (related: rhbz#1065629).

(cherry picked from commit 3dc548476c7e88f7a67cc38daf622631a34e34dd)

Conflicts:
	writerfilter/source/dmapper/DomainMapper_Impl.cxx

Change-Id: I9b2e32c3c7264be0fc1077cb8fb3f1bc5c1955bb
Reviewed-on: https://gerrit.libreoffice.org/8440
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>