State snapshotting doesn't quite work with forks

[marcelo-gonzalez]

If there's a fork at the place where we want to take a state snapshot, there could be an issue where the wrong snapshot is taken. #12912 fixed the fact that the result will be an actually inconsistent state, where unwanted snapshots might not be created, and wanted snapshots might not be created correctly. But there remains an issue where we prioritize the last snapshot request made to the state snapshot actor. But does the last request correspond to the block that will eventually become final? If not, then we might end up with the wrong state snapshot. So, we should fix that, possibly by delaying snapshot creation until the snapshot hash is final