Proto: event emission is not a transaction

Context

!4656 (merged) adds event emission to Michelson through the EMIT instruction. It also adds event addresses in the Destination.t type, though it is not used as a Destination.t and Michelson scripts can do nothing with events addresses, especially CONTRACT do not work on them (and I failed doing it because of annotations, hence we would not be able to make TRANSFER_TOKENS work on events, as suggested in #3228 (closed)).

In this MR:

• I rename Transaction_to_event to Event and change its kind so that it's not a transaction any more
  • leveraging @naih's work on splitting internal operation results, I didn't know it would be useful so quickly.
• I remove the Event case from Destination
• As a consequence: less failure cases that would not happen

@xf6 @tomjack Now I see no point in not including the tag in the hash. So it would be possible if you preferred it.

@shrmtv If we accept this change, it will need to be backported to proto-k to prevent people from storing event address.

Manually testing the MR

Checklist

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