refactor(swingset-vat): move VatData to new vat-data package

[turadg]

closes: #4255 #4830

Description

For #4830 creates a new @agoric/vat-data package to hold the module that wraps the VatData global so that a) it need not be deep-imported and b) it can be imported without depending on the whole @agoric/swingset-vat package in builds. (Sourced only in devDependencies for use in tests.)

For #4255 replaces the use of globals.d.ts with imports from that package.

Shrinks the concessions needed for #4618 (comment)

Defines types for the VatData methods.

Security Considerations

This creates a layer of indirection to access the VatData methods. Whereas the caller previously would request it directly from globalThis now it's requested from a module in a new package which exposes the global value, opening up a supply chain attack.

Documentation Considerations

Increased documentation. Fully backwards compatible.

Testing Considerations

The package has new Ava tests. It also has a type test at src/index.test-d.js per the pattern in https://github.com/SamVerschueren/tsd, though it doesn't make use of the tsd helpers or runner.

[Chris-Hibbert]

I like what I see. I don't have enough of an understanding of this to be the approver

[Chris-Hibbert]

nice!

[dckc]

the packages/xsnap stuff looks fine

[FUDCo]

¡Muy bueno!

[mhofman]

For #4255 replaces the use of globals.d.ts with imports from that package.

I'm late to the party here, but I've been trying to follow the following pattern when switching to exported types:

• all exported types should be available through the base package name. E.g. import('@agoric/vat-data').VatData
• no longer have any exported.js which bring in ambient types

The solution to the first one is usually to have an export * from './src/types.js' in the index.js entrypoint.

Here vat-data doesn't export its types at all. Since it defines its types as a .d.ts file, it can't be used as an export statement directly, and we'd need an intermediate .js file which does a bunch of /** @typedef {import('./types').Foo} Foo */. In general I'd prefer if we stuck to JSDoc as much as possible for now, since most contributors aren't able to maintain pure TS.