resolved fdo#72293 correctly split grouped formulas and regroup

Grouped formulas need to be split at both edges of the deleted area,
regroup _after_ rows have been deleted.

Change-Id: I840806f30cef592e17b4cd3a33c81fd2a8309055
(cherry picked from commit 42f551d524a1df46f6a311d5897ac30bd8fc1aaf)
Reviewed-on: https://gerrit.libreoffice.org/7453
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>