[ddc] Unexpected async ordering on switch cases with no await

[nshahan]

The following code has one case with an await and one that is synchronous. It should and does always execute the synchronous case but it does not execute synchronously as shown by the ordering of the elements in order.

If you replace the switch expression with a ternary expression, the execution appears to happen in the expected order.

import 'dart:async';

void main() async {
  FutureOr<int> value = 3;
  var order = <String>[];
  run() async {
    order.add('Before switch');
    final result = switch (value) {
      Future<int>() => await value,
      int() => value,
    };
    print(result == 3); // Expected: 3
    order.add('After switch');
  }
  var runFuture = run();
  order.add('After run()');
  await runFuture;
  print(order); // Expected: ['Before switch', 'After switch', 'After run()']
}

See flutter/flutter#138306