feat(help): Allow user-provided styled text in StyledStr

[epage]

We are deferring to ANSI escape codes as our external stable API for this. Users can then choose to use owo-colors, color-print, etc as they desire and it will just work thanks to anstream.

anstream is a wrapper around stdout and stderr that will automatically decide whether to

• pass ansi codes through (e.g. unix terminal)
• strip codes (e.g. piped to file)
• convert to wincon API calls (legacy Windows terminal)

By using anstream, we also respect CLICOLOR and CLICOLOR_FORCE. We might have respected NO_COLOR before via termcolor.

I ended up fixing #4431 while at it as I was wanting to debug where the fault was in case it was something to fix in anstream

See #4722
Fixes #1433
Fixes #3108

[epage]

My current thought for how to roll this out is to do it in two steps

1. The switch to anstream
2. The documentation changes around allowing custom styling

This would make it easier to revert the anstream change if its causing problem as we have fewer behavior guarantees around it.

However, since clap is generally used by bins which have committed lockfiles

• It may be a while before people upgrade
• We are more likely to fix any problems immediately and people always have the option to lock to an older version

So maybe we don't need to exercise too much caution and can merge this as-is