Verify we calculate informees correctly in our scala code

[rautenrieth-da]

We have various places where we need to get the informees of a contract from its payload. Among others, bugs in this calculation are problematic because Canton only enforces valid PartyId values for informees. All other PartyId fields may contain strings that are not valid PartyIds.

Recently this lead to ExpiredAmuletAllocationTrigger failing with

java.lang.IllegalArgumentException: Invalid unique identifier `counterparty` with missing namespace.
	at com.digitalasset.canton.topology.UniqueIdentifier$.$anonfun$tryFromProtoPrimitive$1(Identifier.scala:142)
	at cats.syntax.EitherOps$.valueOr$extension(either.scala:95)
	at com.digitalasset.canton.topology.UniqueIdentifier$.tryFromProtoPrimitive(Identifier.scala:142)
	at com.digitalasset.canton.topology.PartyId$.tryFromProtoPrimitive(Member.scala:488)
	at org.lfdecentralizedtrust.splice.sv.automation.delegatebased.ExpiredAmuletAllocationTrigger$$anonfun$$lessinit$greater$1.$anonfun$new$1(ExpiredAmuletAllocationTrigger.scala:50)

, see #6126.

Ideas:

I think ideally we would actually test everywhere that these lists match the stakeholders but I'm not quite sure how to set this up as we don't store stakeholder lists :thinking_face:
maybe a debug mode where we call queryEventById in tests on the ledger API?
the fact that we duplicate that informee computation is also a bit silly