Refactor Simplistic_Editor (#1375)

* refactor out FormattingToolbar and TextEditingDeltaHistoryView from main`

* replace togglebuttonstatemanager and texteditingdeltahistorymanager with appstatemanager

* fix up tests

* clean up

* Add ReplacementTextEditingController to AppState

* formatting

* `dart format`

Co-authored-by: Renzo Olivares <roliv@google.com>
Co-authored-by: Brett Morgan <brettmorgan@google.com>

simplistic_editor/lib/app_state_manager.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/widgets.dart';
+
+import 'app_state.dart';
+
+class AppStateManager extends InheritedWidget {
+  const AppStateManager({
+    super.key,
+    required super.child,
+    required AppState state,
+  }) : _appState = state;
+
+  static AppStateManager of(BuildContext context) {
+    final AppStateManager? result =
+        context.dependOnInheritedWidgetOfExactType<AppStateManager>();
+    assert(result != null, 'No AppStateManager found in context');
+    return result!;
+  }
+
+  final AppState _appState;
+
+  AppState get appState => _appState;
+
+  @override
+  bool updateShouldNotify(AppStateManager oldWidget) {
+    return appState != oldWidget.appState;
+  }
+}