This is a part of #2717
Some settings didn't get getters because
- They are transient parse settings (e.g. ignore errors)
- They get propagated to args and should be checked there
`is_allow_hyphen_values_set` is a curious case. In some cases, we only
check the app and not an arg. This seems suspicious.
`#[clap(about)]` only overrides `about`. If the doc comment also sets
`long_about`, it won't be overridden. This change is to help raise
visibility of reseting `long_about` in these cases.
