Strip FINAL, CONST and ABSTRACT annotations from Dart output

[yjbanov]

They pollute Dart code. Example:

This:

import {
  CONST, FINAL, ABSTRACT
} from 'angular2/src/facade/lang';

@ABSTRACT()
class Blah {
  @FINAL()
  i;

  @CONST()
  constructor(a) {
    this.i = a;
  }
}

Transpiles to this:

library angular2.blah_dart;
import 'package:angular2/src/facade/lang.dart' show CONST, FINAL, ABSTRACT;

@ABSTRACT() 
class Blah {
  final i;
  @CONST() 
  const Blah( a): i = a;
}

(@Final is removed but still imported unnecessarily)

[chalin]

/sub

[mprobst]

Mhpf. Done already, but now this causes dartanalyzer warnings for unused imports :-(

[kevmoo]

@mprobst Now you need to strip the imports. 😄

[mprobst]

Actually handling the unused imports is not feasible at the moment as we don't have precise type information available to detect used and unused imports. So let's just include these in the output for now, and revisit this once we're fully migrated to TypeScript.

Maybe it's easiest to just ignore warnings from the dart analyzer - after all, this is just generated code, and the imports will be dropped by later stages during compilation.