Contracts: Possible bug when a dispute jumps back to a previously used Dispute Kit

[jaybuidl]

Scenario

Round 1 DK1 -> Round 2 DK2 -> Round 3 DK1 again

At round 3, the state of coreDisputeIDToActive and Dispute.jumped might be incorrect at that point in both DK1 and DK2.

⚠️ Attempts at fixing this must ensure that it does not break withdrawFeesAndRewards() which is only called at the end of the last round (so after all the DK jumps).

⚠️ Beware not mix up core/local dispute IDs and core/local round IDs.

Root cause

When jumping to another DK, KlerosCore.appeal() calls DisputeKit.createDispute() which always creates a new Dispute object. Perhaps DisputeKit.createDispute() should be smarter and only create a round if the dispute already exist.