Analyzer: Implement missing methods and new functions quick fix

[matanlurey]

$ dart --version
> Dart VM version: 1.25.0-dev.16.4 (Wed Sep 13 01:47:12 2017) on "macos_x64"

The following:

abstract class GraphVisitor {
  Future<T> visit<T>(T Function<T>() fn);
}

class MyVisitor implements GraphVisitor {}

... will auto-implement the missing GraphVisitor methods incorrectly:

class MyVisitor implements GraphVisitor {
  Future<T> visit<T>(Function fn) {
    // TODO: implement visit
  }
}

[bwilkerson]

https://dart-review.googlesource.com/c/sdk/+/39844