ReadonlyDeep is inconsistent with typescript eslint's isTypeReadonly with regard to readonly sets and map

[RebeccaStevens]

With regard to readonly sets and map, this library's ReadonlyDeep type is not consistent with the isTypeReadonly function from @typescript-eslint/type-utils that is used for eslint rules such as @typescript-eslint/prefer-readonly-parameter-types.

ReadonlyDeep converts Sets and Maps to ReadonlySets and ReadonlyMaps respectively. However, ReadonlySet and ReadonlyMap still have mutable methods. To make these types fully readonly and pass the isTypeReadonly function, the types need to be wrapped in Readonly, e.g. Readonly<ReadonlySet<T>>.

Note: ReadonlyArray doesn't need to be wrapped in Readonly as TypeScript just treats Readonly<ReadonlyArray<T>> the same as ReadonlyArray<T>. i.e. Both have mutable methods. As far as I know there is no way to easily make the methods on an array immutable. The isTypeReadonly function makes an exception for arrays having mutable methods.