Use distinct list of package folders when running pub get
Use distinct list of package folders when running pub get

Otherwise if you have a workspace with overlaps, the same project will come up multiple times and we'll prompt the user even if it's only one unique project.

Fixes #1988.

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