new contracts package, including internal's test utils and Zoe's contractSupport

[turadg]

What is the Problem Being Solved?

There's a growing number of deep imports of @agoric/zoe/src/contractSupport/index.js. We try to avoid deep imports and these ones are so longer they affect readability and line wrapping.

Description of the Design

Move that directory into a new package so they're package-level imports.

Package name: @agoric/contracts. Of course contracts exist in other packages but this is implied to be "SDK for contracts" and the package description will specify: "utilities and sample contracts to support contract development".

Thus the scope will include putting example contracts in the same package: #1656

Security Considerations

Scaling Considerations

Test Plan

• contract supports tools (e.g. for testing) aren't in src. see https://github.com/Agoric/agoric-sdk/pull/7389/files/ad607c012b73c8e932c6930e6c81faa048ae6ed6#diff-3d5e8ede80ff6563788a825af27c4eae07929b4503b20d7d0704a067338d45bf

[erights]

Please not @agoric/support if it remains specific to contracts. How about @agoric/contract-support?

Or, how about @agoric/support and it is not specific to contracts? I suppose it already kinda isn't.

[Chris-Hibbert]

Or move the contracts, too, and call it @agoric/contracts? The contracts need to be moved out of Zoe anyway.

[turadg]

Bumping this up because the versioning of the helpers within the Zoe vat package caused some problems.

For now the client can copy the desired version of contractSupport function instead of importing it. But in the future the client supports should be versioned independently of the backend.