Return JSSymbolRepType from _constructSymbol

Author: nex3

sdk/lib/js_interop/js_interop.dart

@@ -530,7 +530,7 @@ extension type JSBoolean._(JSBooleanRepType _jsBoolean) implements JSAny {}
 extension type JSString._(JSStringRepType _jsString) implements JSAny {}
 
 @JS('Symbol')
-external JSSymbol _constructSymbol([String? description]);
+external JSSymbolRepType _constructSymbol([String? description]);
 
 /// A JavaScript `Symbol`.
 extension type JSSymbol._(JSSymbolRepType _jsSymbol) implements JSAny {