Describe the bug
Assign value to new local variable still makes var when prefer_final_locals present in lint rules

var i = 1 + 2 + 3;

To Reproduce

1. Create project: dart create my_dart
2. Add code: 1 + 2 + 3
3. Refactor code: press keys CMD + .

Expected behavior

final i = 1 + 2 + 3;

Screenshots

Versions (please complete the following information):

• VS Code version: 1.59.1
• Dart extension version: v3.25.1
• Dart/Flutter SDK version: flutter-2.2.3