Fix reduced_index for Integer UnitRanges having eltypes other than Int (#39999)
* reduced_index for BigInt UnitRanges
* Add tests for Integer subtypes
* use OneTo constructor instead of typeof
Co-authored-by: Simeon Schaub <simeondavidschaub99@gmail.com>
Co-authored-by: Simeon Schaub <simeondavidschaub99@gmail.com>