Some async tests are missing asyncStart/asyncEnd

[osa1]

While debugging dart-lang/sdk#54140 @mkustermann realized that some of the async tests in co19 are missing asyncStart and asyncEnd:

• https://github.com/dart-lang/co19/blob/master/Language/Functions/element_type_A02_t03.dart
• https://github.com/dart-lang/co19/blob/master/Language/Functions/element_type_A02_t04.dart
• https://github.com/dart-lang/co19/blob/master/Language/Functions/element_type_A02_t06.dart

When testing in the browser, without asyncStart and asyncEnd, the test driver is not waiting for the test to finish and declaring a success even when the test actually fails.

I quickly searched for all the files with an async main and an asyncStart, and when I compared the outputs I see that there are dozens of files where main is async but the file doesn't have asyncStart. For example:

• LanguageFeatures/Control-flow-collections/dynamic_semantics_list_A03_t02.dart
• Language/Statements/For/Asynchronous_For_in/execution_A02_t01.dart

I used ag -Q 'main() async' -c to find tests with async main and ag -Q 'asyncStart' -c to find the tests with asyncStart. (I think it might make sense to search for await instead of main() async).

[sgrekhov]

@osa1 thank you! I added some missed asyncStart/End(). It's not supposed that all async test should have asyncStart/End(). Tests like

main() async {
  await test1();
  ...
  await test2();
}

don't need asyncStart/End(). But I found a lot of tests that have excessive async.