Regression Statistics: use cell reference, not fix row to calculate offset

Regression Statistics: use cell reference, not fix row to calculate offset

The INDEX() offset was calculated with a fix row number derived
from the initial output position, like 35-ROW(). That fails if the
range later is moved or rows inserted/deleted.

Instead, use a cell reference of the cell's current column and
end row, like ROW($A$34)+1-ROW(). 34+1 to not have things shifted
if a row is inserted before 35.

Change-Id: I11276c4acb35505576daa1a20ad49a4fcdbaba49
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/125914
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins
(cherry picked from commit 324e5c3942870749fae0e62c1c11a1400b772584)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/125897