[dart2js] Update DartFormatter invocations to pass language version.

Bug: #56686
Change-Id: I3f578d29e125426c02eac564ca6baff9fb7d8919
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/384402
Reviewed-by: Bob Nystrom <[email protected]>
Auto-Submit: Nate Biggs <[email protected]>
Commit-Queue: Bob Nystrom <[email protected]>

Author: natebiggs

pkg/compiler/test/tool/graph_isomorphizer/graph_isomorphizer_test.dart

@@ -42,7 +42,9 @@ void unorderedListEquals(List<String> expected, List<String> actual) {
 void verifyGeneratedFile(
     String filename, StringBuffer contents, Map<String, String> expectations) {
   Expect.stringEquals(
-      DartFormatter().format(contents.toString()), expectations[filename]!);
+      DartFormatter(languageVersion: DartFormatter.latestLanguageVersion)
+          .format(contents.toString()),
+      expectations[filename]!);
 }
 
 GraphIsomorphizer generateFiles(List<String> graphFileLines,

pkg/compiler/tool/graph_isomorphizer.dart

@@ -458,7 +458,9 @@ class GraphIsomorphizer {
     var file = File(this.outDirectory + '/' + filename);
     file.createSync(recursive: true);
     var sink = file.openWrite();
-    sink.write(DartFormatter().format(contents.toString()));
+    sink.write(
+        DartFormatter(languageVersion: DartFormatter.latestLanguageVersion)
+            .format(contents.toString()));
     sink.close();
   }