make vat-bank upgradeable

[dckc]

What is the Problem Being Solved?

For the bulldozer upgrade (#6644), all vats need to be upgradeable (#5014). In particular, vat-bank.js, which reflects cosmos x/bank assets into ERTP using the JS/golang bridge.

Description of the Design

#6849 (comment)

Security Considerations

Handling failure modes and such is critical to conservation of assets.

Scaling Considerations

There is performance work scheduled for vat-bank:

• notifying smart wallet of every vbank balance update is too expensive #5896

It might be easier to do that before making it durable, since balance notifiers would go away.
Work to update clients to get balance updates another way (#6788) is coming soon, motivated by #6652 .

Test Plan

Null upgrade test a la #6715 .

cc @ivanlei @michaelfig @erights @warner

[dckc]

just re-discovered #5885 ; this is a dup.