fix(help): Don't show hidden arguments in groups

[julian-klode]

This should be pretty obvious, hidden arguments are shown in groups, but should be hidden

[julian-klode]

Looking for |-- it seems there's no test cases for argument group rendering in the usage but hints welcome (or someone pushing tests, I'm chasing down various rabbit holes 🤣 )

[epage]

Thank you for your patience! I'm getting some time to catch up with my notifications from the US holidays.

Looking for |-- it seems there's no test cases for argument group rendering in the usage but hints welcome (or someone pushing tests, I'm chasing down various rabbit holes 🤣 )

I'm seeing several tests that show the result of format_group:

tests/builder/flag_subcommands.rs
502:Usage: pacman {query|--query|-Q} [OPTIONS]
550:Usage: pacman {query|--query} [OPTIONS]

tests/builder/help.rs
2696:Usage: deno <pos1|--option1> [pos2]

tests/builder/groups.rs
135:  <base|--delete>
137:Usage: clap-test <base|--delete>
162:Usage: clap-test <base|--delete>
192:Usage: clap-test <--all|--delete>
328:  <--in|--spec>
330:Usage: prog --config <--in|--spec>

tests/builder/require.rs
992:Usage: clap-test --opt=<FILE> --foo=<FILE> <--g1=<FILE>|--g2=<FILE>>
1475:Usage: test --require-first <--first|--second>

tests/derive/groups.rs
49:  <CRATES|--path <PATH>|--git <GIT>>
51:Usage: prog --add <CRATES|--path <PATH>|--git <GIT>>
234:  <--path <PATH>|--git <GIT>>
236:Usage: test <--path <PATH>|--git <GIT>>

It would be a big help if you could organize your PR where the commits are

1. Add a test, showing the current behavior (ie it passes)
2. Make the behavior change and update the test