[accounting] New API migration - WORK IN PROGRESS

- Task: https://www.odoo.com/web/#id=9955&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.Uy4wEA7I4G4GwPaU
Suppose in account module, i am going to port this onchange methods to new API (it takes only one argument 'self' itself) But the problem is that when this method is called from another modules view files inside that they pass the parameter explicitly( which are not converted to new api yet - we should not change code on other modules at this time as it will increase diff).

As you mentioned that we should call v8 method from v7 but i don't get how shall we do it as for that we will need to modify 'self' inside v7 and then can call v8 method, i don't think this is the right way to do.
I need your suggestion regarding what to do in such a cases.