[iOS] Remove selectionDidChange call in UndoManager (#45657)

Fixes flutter/flutter#133424

The `-[TextInputDelegate selectionDidChange:]` call actually triggers some unwanted keyboard NLP actions that generate a bunch of candidates and automatically accept the first candidate. This causes `-[UITextInput setMarkedText:selection]` to be called with the first candidate and that inserts extraneous characters after the user types certain characters on the iPad software keyboard.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

shell/platform/darwin/ios/framework/Source/FlutterUndoManagerPlugin.mm

@@ -104,9 +104,9 @@ - (void)setUndoState:(NSDictionary*)dictionary API_AVAILABLE(ios(9.0)) {
     // This is needed to notify the iPadOS keyboard that it needs to update the
     // state of the UIBarButtons. Otherwise, the state changes to NSUndoManager
     // will not show up until the next keystroke (or other trigger).
-    id<UITextInputDelegate> inputDelegate =
-        _viewController.engine.textInputPlugin.textInputView.inputDelegate;
-    [inputDelegate selectionDidChange:_viewController.engine.textInputPlugin.textInputView];
+    UITextInputAssistantItem* assistantItem =
+        _viewController.engine.textInputPlugin.textInputView.inputAssistantItem;
+    assistantItem.leadingBarButtonGroups = assistantItem.leadingBarButtonGroups;
   }
   [self undoManager].groupsByEvent = groupsByEvent;
 }

shell/platform/darwin/ios/framework/Source/FlutterUndoManagerPluginTest.mm

@@ -10,11 +10,13 @@
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngine.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.h"
 
 FLUTTER_ASSERT_ARC
 
 @interface FlutterEngine ()
 - (nonnull FlutterUndoManagerPlugin*)undoManagerPlugin;
+- (nonnull FlutterTextInputPlugin*)textInputPlugin;
 @end
 
 @interface FlutterUndoManagerPluginForTest : FlutterUndoManagerPlugin
@@ -50,7 +52,6 @@ - (void)setUp {
 
 - (void)tearDown {
   [self.undoManager removeAllActionsWithTarget:self.undoManagerPlugin];
-  self.undoManagerPlugin = nil;
   self.engine = nil;
   self.viewController = nil;
   self.undoManager = nil;
@@ -140,4 +141,26 @@ - (void)testSetUndoState {
   XCTAssertEqual(2, delegateRedoCount);
 }
 
+- (void)testSetUndoStateDoesInteractWithInputDelegate {
+  // Regression test for https://github.com/flutter/flutter/issues/133424
+  FlutterViewController* viewController = OCMPartialMock(self.viewController);
+  self.undoManagerPlugin.viewController = self.viewController;
+
+  FlutterTextInputPlugin* textInputPlugin = OCMClassMock([FlutterTextInputPlugin class]);
+  FlutterTextInputView* textInputView = OCMClassMock([FlutterTextInputView class]);
+
+  OCMStub([viewController engine]).andReturn(self.engine);
+  OCMStub([self.engine textInputPlugin]).andReturn(textInputPlugin);
+  OCMStub([textInputPlugin textInputView]).andReturn(textInputView);
+
+  FlutterMethodCall* setUndoStateCall =
+      [FlutterMethodCall methodCallWithMethodName:@"UndoManager.setUndoState"
+                                        arguments:@{@"canUndo" : @NO, @"canRedo" : @NO}];
+  [self.undoManagerPlugin handleMethodCall:setUndoStateCall
+                                    result:^(id _Nullable result){
+                                    }];
+
+  OCMVerify(never(), [textInputView inputDelegate]);
+}
+
 @end