compiler: replace ExternAbi::name calls with formatters

Most of these just format the ABI string, so... just format ExternAbi?
This makes it more consistent and less jank when we can do it.

compiler/rustc_mir_transform/src/function_item_references.rs

@@ -161,12 +161,7 @@ impl<'tcx> FunctionItemRefChecker<'_, 'tcx> {
         let unsafety = fn_sig.safety().prefix_str();
         let abi = match fn_sig.abi() {
             ExternAbi::Rust => String::from(""),
-            other_abi => {
-                let mut s = String::from("extern \"");
-                s.push_str(other_abi.name());
-                s.push_str("\" ");
-                s
-            }
+            other_abi => format!("extern {other_abi} "),
         };
         let ident = self.tcx.item_ident(fn_id);
         let ty_params = fn_args.types().map(|ty| format!("{ty}"));