Sort Private classes before/after public classes in file

[mrgnhnt96]

Is your feature request related to a problem? Please describe. When I organize files that contain multiple classes, it would be nice to sort the classes based on if they're private (just like how the private methods/variables do)

Describe the solution you'd like I think an array of elementOrdering, similar to memberOrdering, could be a possible solution

"flutterStylizer": {
  "elementOrdering": [
      "private-classes",
      "public-classes",
    ],
}