feat: Improve invalid keybind error messages

[otherJL0]

Implementation of Better keybind error messages discussion

[otherJL0]

This PR is a clean implementation of #3727 after mucking up the git history

[mitchellh]

Thanks for this PR. I'm not happy with this approach. I recognize it works, and I recognize the effort, so it does pain me to say this but I'm going to reject this PR. My notes below...

First, I think the errors in general are too generic to add to cli/args.zig. I would recommend re-wrapping them with something like BindingInvalidFormat, BindingInvalidAction, etc.

Still, even with that, it doesn't feel like cli/args should know about these errors. Just spitballing in my head (not sure if its a good approach) but one thing I would try is having a function on T (in parse) that can take an error type E and format it. For example:

pub fn formatError(alloc: Allocator, err: FormatableError) { ... }

And then using hasDecl and some basic Zig reflection to determine if the error matches this error.