[menubar] Plugin does not print Errors

[shyndman]

Hi there,

The menubar plugin handles Exceptions by printing them, but subclasses of Errors slip through the cracks and go unprinted. This is a result of this catch.

Perhaps a fallback catch is warranted, with a print and a rethrow?

[stuartmorgan-g]

I think that was actually a workaround for the fact that we couldn't get responses from native->Dart calls, which has since been fixed; that structure should be revisited. We should see if error conditions get returned at the platform channel level now.