avoid creating zoe ExitObject/SeatHandle cycles in the first place

[warner]

#8401 identified a problem in which every SeatHandle that Zoe creates gets entangled in a cross-vat reference cycle with its ExitObject. PR #8697 improved the situation by severing those cycles every time a Seat is exited or fails, and that code was deployed to the mainnet chain via a vat-zoe upgrade in upgrade-16.

So as of 23-Jul-2024, any Seat that gets exited (or fails) will cut the cycle, and allow the objects to be dropped. That should remove most of the growth related to cycles.

The remaining issue is for Seats that don't exit. To make sure these don't leave cycles around, we need to avoid creating the cycles in the first place. We (@warner and @Chris-Hibbert) have discussed a very different design that would avoid the cycles, but transitioning from the old Kinds to the new ones might be tricky.

This ticket is to track the work for that new design

Originally posted by @warner in #8401 (comment)