[16.0] account_payment_purchase: replace api.onchange by computed field on purchase.order

[alexis-via]

replace api.onchange by computed field on purchase.order
Add company_id in the domain of the fields of purchase.order
Add check_company=True on the 2 fields of purchase.order

[luc-demeyer]

Code review & testing ok.

I am wondering why precompute=True is set on the computed fields.
I tested by changing to precompute=False and the PR works in both cases.
@pedrobaeza
do you think we need precompute=True in this case ?
When reading the doc in the ORM one would think it's required but it seems not to be the case.

[pedrobaeza]

It's because some fields are already precompute, and the dependency chain should be completely that way for avoiding double computing.

[alexis-via]

I also converted (0, 0, {}) to Command.create([})
Ready to merge

[alexis-via]

/ocabot merge major

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[pedrobaeza]

/ocabot merge major

[OCA-git-bot]

What a great day to merge this nice PR. Let's do it!
Prepared branch 16.0-ocabot-merge-pr-1167-by-pedrobaeza-bump-major, awaiting test results.

[OCA-git-bot]

Congratulations, your PR was merged at fc1346a. Thanks a lot for contributing to OCA. ❤️