Promotion onDeactivate side effects get overridden by removeCouponCode

[mschipperheyn]

Describe the bug
When you apply a side effect in onDeactivate for a promotion action, that e.g. saves a values on an orderLine, it gets overridden and cancelled out bc the removeCouponCode, by saving the affectedOrderLines that were loaded before the side effects are executed in applyPriceAdjustments, effectively uses outdated instances of the orderlines to resave those order lines.

To Reproduce
Steps to reproduce the behavior:

1. Create a customField on an orderLine
2. Write a value to it in onActivate
3. Remove the value in onDeactivate
4. Query the database to see it's still there

Expected behavior
Side effects of promotions should not be removed by accident

Environment (please complete the following information):

• @vendure/core version: 3.0.x, 3.1.1

Additional context
Another issue in this context is that a PromotionItemAction runs on an OrderLine but the side effects runs on the entire order. It should also offer additional side effects that just operate on the Item OrderLine

[mschipperheyn]

I have written a fix and I will submit it as soon as I've finished writing tests.