Feat: fish-style abbreviations

[casedami]

Description

Adds support for fish-style abbreviations that are expanded on enter or space. Add them to your config like so:

$env.config.abbreviations = {
  ll: "ls -l",
  gs: "git status"
}

User-facing changes (Release notes)

Added support for fish-style abbreviations that are expanded on enter or space.

Additional notes

supports this reedline feature nushell/reedline#1060

[github-actions]

Hey, just a bot checking in! You edited files related to the configuration.
If you changed any of the default values or added a new config option, don't forget to update the doc_config.nu which documents the options for our users including the defaults provided by the Rust implementation.
If you didn't make a change here, you can just ignore me.

[fdncred]

Thanks @casedami. I'm not sure this is how we want it to work exactly.

Added a conversation on Discord https://discord.com/channels/601130461678272522/615329862395101194/1504176644804579409

How should this feature work?

1. The way it is now, with a hashmap in config (maybe a nushell record)
2. Use a nushell list in the config
3. Point to a file that has a list of abbreviations
4. Add a built-in command like abbr ll ls -al and just call it a doze times for a dozen abbreviations
5. other ideas?

[fdncred]

After yesterday's team meeting we decided on 3 things regarding this PR.

1. The list of abbreviations should be a nushell record in the config.nu
2. We should not have a built-in command like abbr at this point because that would infer that abbreviations work in scripts, which is not the case. They're for the repl only.
3. You should be able to modify the abbreviations at runtime in the repl with $env.config.abbreviations =

If we can get the CI green and make sure these items are followed, we can land this PR.

[casedami]

Ok sounds good, I'll start working on that