Enable validation for extract method/refactor widget for Dart >= 2.17.0
Enable validation for extract method/refactor widget for Dart >= 2.17.0

Landed in https://github.com/dart-lang/sdk/commit/f4b273e782cb02424b975329e54fb9eba9d360cf.

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