Export all internal functions in Distribution.Simple.Utils in .Internal module

Trying to work around #5756 in my Cabal hook, I can't easily make a

```haskell
noticeSay :: Verbosity -> Text -> IO ()
```

using `say` because lots of functions used inside `notice` aren't exported.

Now I have to copy-paste many functions from that module in order to do it; this is wasting a lot of time to get simple things done.

Cabal should export all the useful functions that aren't public API in an `.Internal` module, so that people can use that to work around problems until things get fixed upstream.

Start by reading Distribution.Simple.Utils and the context from issue #5756. Determine which internal functions are intended for an .Internal module and how exposing them would affect Cabal's API boundaries. Done means the requested internal exports are defined with a clear scope and the relevant behavior is covered by the project's tests.

Written by the indexing model from the issue text.