This is used in parsing of meta Contexts across different
modules. This also involved moving to XFastParser for
parsing xml filters in sw, sd, starmath.

Change-Id: Ic663aaac6cb20ee8ce5b97cae87c93220f5a2929
Reviewed-on: https://gerrit.libreoffice.org/42989Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins <ci@libreoffice.org>