This update improves accounting support for cases where electronic invoicing systems do not accept negative invoice lines. It adds helper logic and corrects related tax line splitting so affected invoices can be prepared more reliably.

This PR backport helpers functions from 18.3 used to dispatch negatives lines (for EDI refusing negative lines).
It also backport a fix on _split_base_line().
opw-5382423

Forward-Port-Of: odoo/odoo#245853