[MERGE] purchase_stock: split stock from purchase module

For historical reason, purchase depends on stock module. We now
plan to add purchase feature for services. A service company will
not be interessted by having stock install when they do service
purchases. So this commit breaks this dependency by creating a
new bridge module named 'purchase_stock'.
No functionnal behavior should have changed, this commit only
move code.

However, some points need to be highlighted:
* The purchase report was split, the same way sale report is. Installing
stock will just add a few addionnal informations to the SQL views.
* Since test cases depends on stock demo data, the basic purchase
addon does not contain tests, but this will come in futur tasks.
* consu and service product's receieved quantity can be manually edited,
when stock is not installed. The same mecanism to compute this quantity
done
in sale (for delivered qty) will be implemented later.

Thanks to @amoyaux and @pimodoo for their reviews.

Task #47927