Get keys of tuple T.
Signature:
export type TupleKeys<T extends readonly unknown[]> = T extends readonly [
any,
...infer Tail,
]
? TupleKeys<Tail> | Tail['length'] | `${Tail['length']}`
: neverReferences: TupleKeys
// Expect: 0 | 1 | '0' | '1'
type Keys = TupleKeys<[3, 4]>