fix(types): correctly infer ReadonlyArray types in schema definitions

[vkarpov15]

Fix #12611

Summary

Bitten yet again by the fact that ReadonlyArrays and Arrays are separate classes in TypeScript 😭

Examples

[hasezoey]

LGTM

though i think the old declaration can be replaced, because ReadonlyArray is compatible with Array, but not the other way around

const arr1 = ['test1'];
const arr2 = ['test2'] as const;

type TestR<T extends ReadonlyArray<any>> = T;

const t1: TestR<typeof arr1> = arr1; // works
const t2: TestR<typeof arr2> = arr2; // works

type TestW<T extends Array<any>> = T;

const t3: TestW<typeof arr1> = arr1; // works
const t4: TestW<typeof arr2> = arr2; // error "trying to assign readonly to mutable type"

[vkarpov15]

@hasezoey I tried removing extends (infer Item)[], tests fail. So it doesn't look like we can remove the declaration after all.