Upgrade XS to 3.8

[mhofman]

What is the Problem Being Solved?

Moddable SDK 3.8 will include a patch to hide organic gc from liveslots, in order to workaround #6748

We need to update before the Bulldozer upgrade since that will change the transcripts shape.

Description of the Design

Update to Moddable SDK 3.8

Security Considerations

None

Scaling Considerations

None

Test Plan

Follow steps adapted from #6929

I have a follower with a pismoC fork + organic gc patch that can be used to directly get vat transcripts instead of regenerating the vat transcripts from a chain transcript with the updated XS version. That will confirm that the new version is fully behavior compatible.