CI check generate code (#4998)

* call reflection code generation from tests

This simplifies instructions to contributors so they don't forget to update
reflection code.

* add error handling to generate_code scripts

Let them propagate their errors instead of swallowing them so they show
up when called in CI.

* apply editorconfig to shell scripts

* use ordered map in dart codegen

Using an unordered map in the codegen can lead to spurious diffs in the
generated dart code.

* add CI check for generate_code being run

* update reflection_generated.h

* disable diff-check for monster_test.bfbs

Work around #5008.
diff --git a/tests/monster_test_my_game.example2_generated.dart b/tests/monster_test_my_game.example2_generated.dart
index 857e66d..eed14bc 100644
--- a/tests/monster_test_my_game.example2_generated.dart
+++ b/tests/monster_test_my_game.example2_generated.dart
@@ -6,8 +6,8 @@
 import 'dart:typed_data' show Uint8List;
 import 'package:flat_buffers/flat_buffers.dart' as fb;
 
-import './monster_test_my_game.example_generated.dart' as my_game_example;
 import './monster_test_my_game_generated.dart' as my_game;
+import './monster_test_my_game.example_generated.dart' as my_game_example;
 
 class Monster {
   Monster._(this._bc, this._bcOffset);