The exposition-only type trait `pair-like` includes `ranges::subrange`,
but in every single case excludes `ranges::subrange` from the list. This
patch introduces two new traits `__tuple_like_no_subrange` and
`__pair_like_no_subrange`, which exclude `ranges::subrange` from the
possible matches. `__pair_like` is no longer required, and thus removed.
`__tuple_like` is implemented as `__tuple_like_no_subrange` or a
`ranges::subrange` specialization.
