impl Step for char
impl Step for char

Enables Range<char> to be iterable

Note: https://rust.godbolt.org/z/fdveKo
An iteration over all char ('\0'..=char::MAX)
includes unreachable panic code currently.
Updating RangeInclusive::next to call
Step::forward_unchecked (which is safe to do
but not done yet becuase it wasn't necessary)
successfully removes the panic from this iteration.

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust