Maintain order of yielded claim events

Maintain order of yielded claim events

Since the claim events are stored internally within a HashMap, they will
be yielded in a random order once dispatched. Claim events may be
invalidated if a conflicting claim has confirmed on-chain and we need to
generate a new claim event; the randomized order could result in the
new claim event being handled prior to the previous. To maintain the
order in which the claim events are generated, we track them in a Vec
instead and ensure only one instance of a PackageId only ever exists
within it.

This would have certain performance implications, but since we're
bounded by the total number of HTLCs in a commitment anyway, we're
comfortable with taking the cost.