'cabal check' or 'cabal sdist' ought to warn about non-ASCII characters

**Describe the feature request**

Hackage [rejects tarballs that contain non-ASCII filenames](https://github.com/haskell/hackage-server/blob/8815bc9e27ec25506952f6e41b38d5293d5d31d6/src/Distribution/Server/Packages/Unpack.hs#L467-L470), but neither `cabal check` nor `cabal sdist` complains. I suggest that one of these (probably `cabal check`) is modified to complain.

**Additional context**

A user (or bit of automation) can get quite far in a release process before encountering this at the very end.

Start by tracing the implementations of `cabal check` and `cabal sdist`, then compare their validation behavior with Hackage's rejection of non-ASCII filenames in the linked unpacking code. Done means the relevant command warns about such filenames before the release process reaches Hackage.

Written by the indexing model from the issue text.