Enable checkJs to switch opt-in to opt-out for tsc

[turadg]

What is the Problem Being Solved?

Many files in the repo aren't type checked at all because they don't have @ts-check and our tsc compiler options are just to allowJs (implied by using jsconfig.json).

Description of the Design

Enable checkJs option (ref) which "is the equivalent of including // @ts-check at the top of all JavaScript files which are included in your project".

Note that this is blocked on #4560 because anything greater than the default maxNodeModuleJsDepth of zero means enabling checkJs will make tsc check inside the node_modules directory.

Security Considerations

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Test Plan

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[turadg]

More more motivation: the @ts-check makes js apps that have SDK packages in node_modules re-check them. I haven't devised a way to prevent this other than patching the packages: Agoric/wallet-app@7cad807

[mhofman]

Weird, I didn't think tsc reported issues in node_modules path. Also to clarify, I suppose this wouldn't be a problem if all SDK packages had correctly exported types using generated .d.ts files?

Aka if we solved #6343

[turadg]

Weird, I didn't think tsc reported issues in node_modules path

Example:

Errors  Files
     4  ../../node_modules/encoding/lib/encoding.js:59
    60  ../../node_modules/node-fetch/lib/index.js:3
     4  src/main.js:4

Many have more than that.

I suppose this wouldn't be a problem if all SDK packages had correctly exported types using generated .d.ts files?

I think that's right, because the .d.ts files would be read instead. But I'm not certain because I think I've seen some Endo packages that were converted over still have the problem. e.g. I think iI saw an error forbundle-source, though that's probably due to SDK being on the latest release (not dev) which lacks the types builds.