Make `debug_name()` on simple `Identifier` items (Enum, TypeAlias) a fast Rc clone.

PiperOrigin-RevId: 524105545
diff --git a/rs_bindings_from_cc/ir.rs b/rs_bindings_from_cc/ir.rs
index 290eb55..245d576 100644
--- a/rs_bindings_from_cc/ir.rs
+++ b/rs_bindings_from_cc/ir.rs
@@ -614,7 +614,7 @@
         self.id
     }
     fn debug_name(&self, _: &IR) -> Rc<str> {
-        self.identifier.to_string().into()
+        self.identifier.identifier.clone()
     }
     fn source_loc(&self) -> Option<Rc<str>> {
         Some(self.source_loc.clone())
@@ -646,7 +646,7 @@
         self.id
     }
     fn debug_name(&self, _: &IR) -> Rc<str> {
-        self.identifier.to_string().into()
+        self.identifier.identifier.clone()
     }
     fn source_loc(&self) -> Option<Rc<str>> {
         Some(self.source_loc.clone())