Make slash commands more discoverable (#12480)

<img width="648" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/a63df904-fbbe-4e0a-80b2-c98ebee90690">

Release Notes:

- N/A

Co-authored-by: Nathan <nathan@zed.dev>

crates/extension/src/extension_slash_command.rs

@@ -27,7 +27,7 @@ impl SlashCommand for ExtensionSlashCommand {
         self.command.description.clone()
     }
 
-    fn tooltip_text(&self) -> String {
+    fn menu_text(&self) -> String {
         self.command.tooltip_text.clone()
     }