After fish 4.1 released, fish completion scripts should parse the command line by using `read` instead of by using `commandline`

[rgoldberg]

After fish 4.1 released, fish completion scripts should parse the command line by using read instead of by using commandline.

commandline is broken. read, but not commandline, has supposedly been fixed to properly parse command lines for the upcoming fish 4.1.

Must either redo scripts to use read for all versions of fish (expecting better data and/or more options in 4.1+), or use read for only 4.1+, but continue to use commandline for older fish versions.

ArgumentParser version: main
Swift version: n/a

Checklist

• If possible, I've reproduced the issue using the main branch of this package
• I've searched for existing GitHub issues

Steps to Reproduce

Try completing a custom completion command line token in fish where you have redirects in the command line.

Expected behavior

Redirects should be included in the [String] that represents the command-line tokens.

Actual behavior

Redirects are not included in the [String] that represents the command-line tokens.

See #679 (comment), and potentially other comments on that issue, for some info about how fish command-line parsing is broken, amongst tons of other info.