Implement more client-sided autocomplete suggestions

[StayBlue]

This is part two of my original PR #1853, and an implementation of the suggestion in my issue #1353 (for at least the client-side portion).

The initial goal of that issue was mainly to handle the client-side, so if anyone ever wants to tackle that problem themselves, they can (but I probably won't).

This PR has both good and bad aspects.

The good:

• If valid autocomplete suggestions cannot be found for the given argument, it will not return any matches.
• This iteration now passes in the command as one of the arguments.
• This iteration now passes in the argument correctly.

The bad:

• This implementation likely does not alleviate the concerns raised here.
  • This has a lot of Regex that runs every time you type something into any argument field (which, by the way, I generated with AI, so I have no idea if it even works beyond what I tested).
• This implementation is over-engineered for the job, especially the ParseArg function.
  • This trades performance for extensibility.
• There's a lot of logic in the Autocomplete function.
  • It might benefit from some more abstraction.
• This implementation (still) only does anything if you use the Default theme.

[StayBlue]

I'm marking this as a draft since I don't have proof-of-functionality yet. I would also like to get some eyes on this to see where I should take it from here.

[StayBlue]

This PR hasn't received as much visibility as I had hoped, so I will unmark it as a draft. However, it shouldn't be merged until there's more feedback on it.

[StayBlue]

Proof-of-functionality:
https://github.com/user-attachments/assets/337c1594-29d8-4aab-af4d-fbaa1c063dec

[GalacticInspired]

RobloxStudioBeta_eDvSf1ASEm.mp4

it's doing this whenever i click tab, either removing the player name or switching to a different command

[Dimenpsyonal]

Merge conflict :(