Cherry-pick xsnap fixes for next chain upgrade

[mhofman]

What is the Problem Being Solved?

agoric-sdk is stuck on a fork of Moddable SDK 3.8.7 until we figure out our xsnap-worker upgrade story (see #6361).

In the meantime, some fixes landed in XS that do not affect behavior of programs that have executed on chain, and are thus safe to include in a software upgrade (technically they would be safe to be applied as a non consensus patch).

Description of the Design

Cherry pick fuzzing and similar fixes that have landed in the Moddable SDK.

Security Considerations

The goal is to remove the possibility that a permissioned contract would trigger buggy XS behavior in the future, simplifying audits.

Scaling Considerations

None

Test Plan

Moddable SDK up until 4.1 has been acceptance tested (see #6929) against pismo transcripts. Some fixes landed after that version. We should also run against current mainnet transcripts

Tasks

Beta Give feedback

1. Run acceptance tests against current pismo transcripts
2. Run acceptance tests against current mainnet transcripts (Blocked by Update vat transcript extract and replay tools to post bulldozer #8494)

Upgrade Considerations

The fixes must not affect the observable execution of existing deployed programs. Since the upgrade will be done in consensus, it is allowed too affect the content of snapshots and the metering of execution, but that is not expected to be the case.