Debugger doesn't break on unhandled exceptions from rethrow

[DanTup]

This might be a dupe of #29550, but I'm not sure since it's a rethrow and there's no finally involved (I think the behaviour of both is unexpected, perhaps questionable).

Given this code:

main() {
  try {
    num.parse('a');
  } on Exception {
    rethrow;
  }
}

If you run with "break on unhandled exceptions", the debugger never breaks, but you get a crash. My interpretation is that the exception being raised by rethrow is unhandled (hence the crash) and should break the debugger.

It is my belief that (at least) JavaScript, C#, Java would all break there.