Add `new_range_api` for RFC 3550
Initial implementation for #125687
This includes a `From<legacy::RangeInclusive> for RangeInclusive` impl for convenience, instead of the `TryFrom` impl from the RFC. Having `From` is highly convenient and the debug assert should find almost all misuses.
This includes re-exports of all existing `Range` types under `core::range`, plus the range-related traits (`RangeBounds`, `Step`, `OneSidedRange`) and the `Bound` enum.
Currently the iterators are just wrappers around the old range types.
Tracking issues:
- https://github.com/rust-lang/rust/issues/123741
- https://github.com/rust-lang/rust/issues/125687
9c8a88996e