Let Clap wrap help texts automatically

[mgeisler]

This makes the rustup help show and other help texts much more readable on my terminal.

This enables the optional wrap_help feature in Clap. For me, rustup help show looks like this without the feature:

With wrap_help, I see

I find the second much nicer to read. (I'm a fan of wrapping lines, I maintain the underlying Textwrap library used by Clap 😄)

[Rustin170506]

I tested it on my macOS. It worked well.

Thanks!

[Rustin170506]

I have a question: does this help for #2920? Because I found it still broken the line.

[mgeisler]

Hi @hi-rustin, thanks for testing it!

I'm afraid the fix for wrapping URLs was only released in Clap 3.1.16, and Rustup is still using Clap 2.

So perhaps I could work on updating to the new Clap version first?

[mgeisler]

Hah, it turns out that @zohnannor has prepared the Clap update already in #3064.

[Rustin170506]

Hi @hi-rustin, thanks for testing it!

I'm afraid the fix for wrapping URLs was only released in Clap 3.1.16, and Rustup is still using Clap 2.

So perhaps I could work on updating to the new Clap version first?

Got it. Thanks!

[Rustin170506]

r? @kinnison Could you please take a look? It looks good to me. Thanks!