Create a dev/test utils package

[turadg]

What is the Problem Being Solved?

In many cases packages depend on each other for exports only need for development or testing. This increases the cycles in the dependency graph: #4645

It also makes it more work to maintain semantic version discipline and can lead to hacks like not declaring dependencies (example in #5232 )

Description of the Design

Create a package that gathers up exports that needed only for development or testing.

Trim down the exports of the primary packages. For example, @agoric/swingset-vat may be able to just export makeFakeVirtualStuff in place of tools/.

Security Considerations

Isolates test/dev code.

Test Plan

CI