InsertCurrentTime: in input mode inherit matching format if set

In case a date or time cell format was set, inherit that format for
Ctrl+; or Ctrl+: date/time insertion while editing the cell.

Change-Id: If13e680fc74ab36611f8c11d992dba4b9c91ddb4
(cherry picked from commit 980fd719648fb5b7cbe93ba23c1ee2f180ffcee8)
Reviewed-on: https://gerrit.libreoffice.org/11893
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>