305ca05cbe
feat(byte_sub_ptr): unstably add ptr::byte_sub_ptr This is an API that naturally should exist as a combination of byte_offset_from and sub_ptr both existing (they showed up at similar times so this union was never made). Adding these is a logical (and perhaps final) precondition of stabilizing ptr_sub_ptr (https://github.com/rust-lang/rust/issues/95892). Original PR by ``@Gankra`` (https://github.com/rust-lang/rust/pull/121919), I am just reviving it. The 2nd commit (with a small docs tweak) is by me.