complete/zsh: improve --hyperlink-format completion

Also don't re-define helper functions if they exist.

Closes #3102

crates/printer/src/hyperlink/mod.rs

@@ -190,6 +190,7 @@ impl std::fmt::Display for HyperlinkFormat {
 #[derive(Clone, Debug)]
 pub struct HyperlinkAlias {
     name: &'static str,
+    description: &'static str,
     format: &'static str,
     display_priority: Option<i16>,
 }
@@ -200,6 +201,11 @@ impl HyperlinkAlias {
         self.name
     }
 
+    /// Returns a very short description of this hyperlink alias.
+    pub const fn description(&self) -> &str {
+        self.description
+    }
+
     /// Returns the display priority of this alias.
     ///
     /// If no priority is set, then `None` is returned.