ReadonlyTuple: Deprecate in favour of TupleOf

[som-sm]

Now that we have TupleOf exposed, I don't think we need a separate ReadonlyTuple type because it simply wraps the result of TupleOf in Readonly.

This PR also refactors the implementation of ReadonlyTuple to use TupleOf, which in turn fixes the following bug wherein the type wasn't distributing over the Length argument.

type Current = ReadonlyTuple<string, 3 | 4>;
//=> readonly [string, string, string]

type Fixed = ReadonlyTuple<string, 3 | 4>;
//=> readonly [string, string, string] | readonly [string, string, string, string]

[sindresorhus]

Maybe worth adding it to https://github.com/sindresorhus/type-fest?tab=readme-ov-file#alternative-type-names too?

[som-sm]

Maybe worth adding it to https://github.com/sindresorhus/type-fest?tab=readme-ov-file#alternative-type-names too?

Yeah, I thought this too, but do you wanna add this now or after we have removed the type?

[sindresorhus]

We can just do it now. When I type is deprecated, we can just pretend it doesn't exist.