[Wilds] Update "arc shell-complete" for toolsets

Summary:
Ref T13098. Major changes:

arc shell-complete now installs itself to your ~/.profile. Running arc shell-complete again will update the hook and update the completion rules.

Completion rules work for all toolsets, so you can install once and then autocomplete in arc, phage, etc.

This code supports other shells in theory, and I developed most of it with ZSH support next to the Bash support. However, while actually testing ZSH support, I couldn't get it to even slightly work and found myself falling down a very, very deep rabbit hole of ZSH being entirely written in bash script and ${0:a:h} being a legitimate script construction. The existing ZSH support comes from one guy in 2012 and also does not work for me on master, so I ultimately removed it. Open to restoring it but I wasn't able to figure it out in 10 minutes of Googling and I'm not convinced it's worth 11 minutes of Googling.

I left a few rough edges here with notes on how to improve/fix them, but the basics all work.

Test Plan:

• Ran arc shell-complete under various stages of ~/.profile, couldn't get it to do anything bad.
• Ran arc lib<tab>, arc shell-complete --curr<tab>, etc. Got sensible suggestions and completions.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13098

Differential Revision: https://secure.phabricator.com/D19700