Rollup merge of #104353 - clarfonthey:cstr-bytes-iter, r=cuviper

Add CStr::bytes iterator

See rust-lang/libs-team#135 for an ACP.

Since rust-lang/libs-team#134 was also accepted, this type is now `core::ffi::c_str::Bytes` instead of `core::ffi::CStrBytes`.

Author: matthiaskrgr