fix #29228, let* precedence should match generated expression

pkg/dev_compiler/lib/src/compiler/js_metalet.dart

Index: pkg/dev_compiler/lib/src/compiler/js_metalet.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
index 39478841d23d1dc93f736ca307175eb03e83f0d1..07f4615fabaf657f3dcfe410de651fb55e71bf43 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
@@ -143,7 +143,7 @@ class MetaLet extends Expression {
   }
 
   /// This generates as either a comma expression or a call.
-  int get precedenceLevel => variables.isEmpty ? EXPRESSION : CALL;
+  int get precedenceLevel => toExpression().precedenceLevel;
 
   /// Patch to pretend [Template] supports visitMetaLet.
   Instantiator _templateVisitMetaLet(InstantiatorGeneratorVisitor visitor) {