[FIX] stock: no tracking for service product

Steps to reproduce the bug:
- Create a storable “P1”:
   - tracking= serial
   - save
- Change the type of product to service

Problem:
some fields for tracked products are not hidden, because the product
tracking is not updated.

Solution:
Convert _onchange_type into compute methods.
The tracking is updated even if the change type is applied from the
"product.product" form.

opw-3499976

closes odoo/odoo#136451

X-original-commit: 495d5b555e69a319b48485e96a6ca4b61fb32347
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Djamel Touati (otd) <otd@odoo.com>