New lint: Avoid unstable final fields

example/all.yaml

@@ -43,6 +43,7 @@ linter:
     - avoid_types_as_parameter_names
     - avoid_types_on_closure_parameters
     - avoid_unnecessary_containers
+    - avoid_unstable_final_fields
     - avoid_unused_constructor_parameters
     - avoid_void_async
     - avoid_web_libraries_in_flutter

lib/src/rules.dart

@@ -48,6 +48,7 @@ import 'rules/avoid_type_to_string.dart';
 import 'rules/avoid_types_as_parameter_names.dart';
 import 'rules/avoid_types_on_closure_parameters.dart';
 import 'rules/avoid_unnecessary_containers.dart';
+import 'rules/avoid_unstable_final_fields.dart';
 import 'rules/avoid_unused_constructor_parameters.dart';
 import 'rules/avoid_void_async.dart';
 import 'rules/avoid_web_libraries_in_flutter.dart';
@@ -279,6 +280,7 @@ void registerLintRules({bool inTestMode = false}) {
     ..register(AvoidTypesAsParameterNames())
     ..register(AvoidTypesOnClosureParameters())
     ..register(AvoidUnnecessaryContainers())
+    ..register(AvoidUnstableFinalFields())
     ..register(AvoidUnusedConstructorParameters())
     ..register(AvoidVoidAsync())
     ..register(AvoidWebLibrariesInFlutter())