[vm/nnbd] Use legacy types to create lists in Dart_NewListOf

In order to be backwards-compatible existing Dart API should create
lists using legacy types (instead of lists of non-nullable types).

Issue: #40176
Change-Id: Ie5460b41b2c5e9ecfb124bce1ab43fd466930ea0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135531
Reviewed-by: Ryan Macnak <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>

Author: alexmarkov

runtime/vm/dart_api_impl.cc

@@ -2827,9 +2827,9 @@ static RawTypeArguments* TypeArgumentsForElementType(
     case Dart_CoreType_Dynamic:
       return TypeArguments::null();
     case Dart_CoreType_Int:
-      return store->type_argument_int();
+      return store->type_argument_legacy_int();
     case Dart_CoreType_String:
-      return store->type_argument_string();
+      return store->type_argument_legacy_string();
   }
   UNREACHABLE();
   return NULL;