[FIX] contract: Don't execute onchange after invoice creation
[FIX] contract: Don't execute onchange after invoice creation

Using that approach (that is the current one in core)  has a lot of side effects and
performance bottlenecks. You can read odoo/odoo#40156 for summarizing them.

This also improves the handling of the values of payment term an fiscal position
for using the partner ones if not set.

OCA/contract,OCA/contract,OCA/contract