Convert keymap context to use generics and Cow<'static> so we don't have to add .to_string() and .into() for each usage

crates/project_panel/src/project_panel.rs

@@ -1314,7 +1314,7 @@ impl View for ProjectPanel {
 
     fn keymap_context(&self, _: &AppContext) -> KeymapContext {
         let mut cx = Self::default_keymap_context();
-        cx.set.insert("menu".into());
+        cx.add_identifier("menu");
         cx
     }
 }