[IMP] account: improve display name of cancelled journal entries

The display name of cancelled entries is "/"
This provides no information to the user - especially when the duplication message is logged.

This aims to improve the display_name of account.move so draft and cancelled entries display the id as a reference

closes odoo/odoo#70764

Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>