dartfmt should fix formatting issues reported by Pub website / pana package

[cedx]

Pub website has started to lower the score of packages with some formatting issues.

Me, and probably a lot of developers, will not change their coding style just because the Dart team has decided that our code was not properly formatted.

So, dartfmt should fix these errors in order to help package publishers to meet the new requirements of Pub website / pana analyzer.

See: dart-lang/pub-dev#2322

[natebosch]

The pub-dev issue calls out braces around line-wrapped conditional bodies and included links to issues in this repo discussing it. I don't see other specific questions in that thread.

I reopened #664 to start a discussion about whether we can add a --fix flag for that one specifically. If there are other formatting issues that are checked by pana that you believe would fit as a --fix please open specific issues for them - a blanket issue isn't actionable.