Add value hints to command line arguments to improve shell completion accuracy

[EliteTK]

Summary

This partially addresses #17076 by adding value_hint to various arguments.

For cases where an option takes a path to either specifically a file or a directory directory, ValueHint::FilePath and ValueHint::DirPath are used respectively to try to limit the amount of noise presented by completions in shells which support it.

For cases where a URL (and only a URL, not a path) can be supplied, ValueHint::Url is used.

For cases where a python interpreter is to be specified, ValueHint::CommandName is used which will tab complete from $PATH by default, but will fall back to completing executable filenames if you start typing a path.

Finally, for the many cases where there is no built in completion which would make sense, and where default completion of a path would make no sense (e.g. a package name, or version specifier, or date) ValueHint::Other is used to explicitly disable completion.

Test Plan

Manually tested a bunch of these. These could be automated in the sense that we could snapshot the completion from zsh but I've not thought about how that could be done yet.

[konstin]

Not deep into how shell completions work, but the code looks good.

[zanieb]

I think --python <version> is the most common use-case here, not passing an executable name.

[EliteTK]

The thought process here was that if someone wants to type a version they can still do so, and we have no particular way to complete them, but if they did want to specify a python executable instead, they would have an easier time due to completions being restricted to valid executables.

The default here is to do "_default" completion on zsh, which will complete files and things like that. So CommandName actually restricts this to fewer things.

The only alternative I can think of is to make this ValueHint::Other but this would prevent zsh from ever letting you complete paths to programs or programs in your path.

What do you think?

[zanieb]

I think we should probably use Other. I don't want to encourage people to use Python executables from their PATH here, I think that's rarely a desirable pattern and can be confusing.

[EliteTK]

Fair enough, will change these.

[zanieb]

Editables are local directories

[EliteTK]

I can't remember why I chose ValueHint::Other here ... I think I went into looking what an editable was and found that it could be a directory or some weird syntax. But that doesn't really justify not letting you complete directories.

Will fix.