Jsonify: handle unknown as JsonValue

[GerkinDev]

Closes #1195 by mapping unknown to JsonValue. If requested, I can preserve unknown as mentioned in the issue

Had a bit of struggles with the test

declare const tupleStringJson: Jsonify<string[] & ['some value']>;
expectType<['some value']>(tupleStringJson);

because

type JsonifyList<T extends UnknownArray> = T extends readonly [infer F, ...infer R]

infered {F: 'some value', R: unknown[]}, thus the arguably not ideal hack. Yet, it passes all the tests and it somewhat makes sense.

This problem looks like a known issue in TS tuples handling & intersection with arrays, but depending on the POV, it may be more of a feature than a bug.

[GerkinDev]

Given how any is handled I suppose it makes sense

[sindresorhus]

If requested, I can preserve unknown as mentioned in the issue

Let’s not preserve unknown. Jsonify’s job is to produce something assignable to JsonValue, so mapping unknown to JsonValue keeps the contract clear and makes it more
ergonomic without sacrificing soundness.