Support for Utf8Path TempFile and TempDir?

[sunshowers]

Hi there --

I'm the primary maintainer of camino, a popular Rust library for UTF-8 paths. I'm wondering if you were interested in adding support for it to tempfile.

This could be behind an optional feature.

We could add:

• Builder::utf8_tempfile/Builder::utf8_tempfile_in and NamedUtf8TempFile
• Builder::utf8_tempdir/Builder::utf8_tempdir_in and Utf8TempDir

These methods could continue to return io::Error, and if conversion to UTF-8 isn't successful could return an InvalidData variant with more information in the payload, similar to canonicalize_utf8.