Function all_key_names 

pub fn all_key_names<A: ActionSet>(keys: HelpKeys<'_, A>, action: A) -> String

Every key for action, joined with / (e.g. f/j/Enter/Space): its slots in Keymap::chords_for order, then its fixed keys (Keymap::fixed_chords_for). On a controller, every button for it (Keymap::buttons_for). HelpKeys::not_mapped if its slots are empty.