Reapply rules to split transactions when the parent changes (#2834)

* Reapply rules to split transactions when the parent changes

Concretely, this enables the "standard" workflow for
split-transaction-entry on desktop, where you enter the payee first, and
then edit the amount afterwards (and expect splits in a rule to apply when
you edit the amount).

* Add release notes

* Fix bug in first field below parent transaction

* Update vrt