fdo#68959: sw: fix painting of tab fill characters in small caps text

The member SwDrawTextInfo::pPos was changed from a pointer to some
externally provided Point to a real object; unfortunately there were
some functions which hold backups of the current pPos as a
reference/pointer and then restore it, and the restore is a no-op now.
So use real Points as backups.

(regression from f22006dc6ac34a35a060e15466cf6b2d2058617d)

Change-Id: I8470143ec494cb194a88ddcbd12d96867974278f
(cherry picked from commit c445d40da8daa2f6ec0ae9930a06f50ab80cc85d)
Reviewed-on: https://gerrit.libreoffice.org/7567
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>