Allow detection of Dart SDK from flutter even for non-Flutter projects
Allow detection of Dart SDK from flutter even for non-Flutter projects

But only as a last resort (this is what will be hit for
flutter.createProject if Dart wasn't on PATH).

Fixes #630.

Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code