Allow pattern matching on error handling

[rubenferreira97]

With the recent introduction of pattern matching in Dart, it would be beneficial to extend this feature to error handling, enabling more expressive and concise error handling mechanisms.

This proposal aims to leverage pattern matching syntax for catching exceptions, providing developers with more flexibility and clarity in error handling while aiming to solve #112.

Straw man syntax:

class FooException implements Exception {
  final String msg1;
  FooException(this.msg1);
}

class BarException implements Exception {
  final String msg2;
  BarException(this.msg2);
}

void main() {
  try {
    throw FooException('Hi!');
  } catch (e case FooException() || BarException(), StackTrace s) {
    print('Exception is FooException or BarException');
  } catch (e case FooException(msg1: final m) || BarException(msg2: final m) when m.length > 0, s) {
    print(m);
  }
}

Since there are no checked exceptions in Dart, we cannot exhaustively check for exceptions.