Add apply command

[pingiun]

Description

Fixes #7758

Adds a new command to call internal or external commands with arbitrary arguments.

Usage example:

let commandname = "sl"
let args = []
apply $commandname $args

User-Facing Changes

Add a new command

Tests + Formatting

This is a WIP, tests will be added later

After Submitting

This will need some nice documentation

[kubouch]

Thanks for looking into it. This will work for external commands but to make it work with internal commands, you'd need to make apply a parser keyword and then figure out how to pass flags to it with type checking -- this would need some additional design.

Since external commands were solved by allowing blocks to extern, the remaining problem is how to pass flags to internal commands. With the core team, we settled on allowing "traditional" call syntax (e.g., foo --bar would be equal to foo(bar: true), I wrote it up here: #9116.

Also for externals, you can use ^$commandname $args, seems like apply is not necessary in this case.

[fdncred]

@pingiun Were you going to try to work within Kubouch's comments or should we close this for now?

[pingiun]

let’s close this for now

[fdncred]

ok, thanks. we appreciate you trying to make nushell better!!!