AbstractFilePath support

https://github.com/haskell/filepath/pull/103

AFPP will hit filepath sometime soon. What remains to be done is adding support for it in unix and Win32 (I have patches for those).

It will not be included in base, since the earliest GHC version that could support it is 9.6.

What I'm looking for now is an alternative Prelude that is willing to support AFPP, so I can (aggressively) market said prelude in filepath.

Any such prelude would very likely have to additionally depend on unix/Win32 and add functions like `openFile :: AbstractFilePath -> IO Handle`, `withOpenFile`, etc.

I have my own file io library that has preliminary patches for AFPP and could be salvaged for such efforts: https://github.com/hasufell/hpath/tree/abstract-filepath/hpath-directory

Any opinions?

Start by reviewing filepath PR 103 and the abstract-filepath branch of hpath-directory, then assess whether relude should provide an alternative Prelude with AbstractFilePath support. The issue is done only when the scope and required unix/Win32 dependencies and file-I/O API are agreed and implemented.

Written by the indexing model from the issue text.