Support getting files etc. in const

[ModProg]

Not sure if this is achievable witht the current architecture, but I would like to be able to query files in const. Hopefully this gets done in the need future so I could then also unwrap the resulting file: rust-lang/rust#67441.

[Michael-F-Bryan]

The Dir::entries() getter is const, so you should already be able to look up files at compile time.

You'd need to write your own recursive search function though. I don't think the existing methods for looking up items (e.g. Dir::get_file()) can be made const because they take some S: AsRef<Path> and traits aren't allowed in const contexts yet.

[ModProg]

Alright, makes sense.