[iOS] Fix App crash when use WebView with iOS VoiceOver (#52484)

This PR fix the issue [flutter/flutter
#140528](flutter/flutter#140528).

This fix cleans up declarations regarding `retain` and `release`.
`flutterAccessibilityContainer` needs to be managed in
`FlutterPlatformViews.mm`, and problems will occur if `retain` or
`release` is performed in `SemanticsObject.mm`.

This fix is checked by the `testFlutterPlatformViewSemanticsContainer`
function in the `SemanticsObjectTest.mm`.
The result is not changed.

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responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or the PR is [test-exempt]. See [testing the engine] for
instructions on writing and running engine tests.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

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Author: tacck

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

@@ -981,10 +981,6 @@ @implementation FlutterTouchInterceptingView {
   fml::scoped_nsobject<DelayingGestureRecognizer> _delayingRecognizer;
   FlutterPlatformViewGestureRecognizersBlockingPolicy _blockingPolicy;
   UIView* _embeddedView;
-  // The used as the accessiblityContainer.
-  // The `accessiblityContainer` is used in UIKit to determine the parent of this accessibility
-  // node.
-  NSObject* _flutterAccessibilityContainer;
 }
 - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
              platformViewsController:
@@ -1063,14 +1059,15 @@ - (void)touchesCancelled:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
 - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
 }
 
-- (void)setFlutterAccessibilityContainer:(NSObject*)flutterAccessibilityContainer {
-  _flutterAccessibilityContainer = flutterAccessibilityContainer;
-}
-
 - (id)accessibilityContainer {
   return _flutterAccessibilityContainer;
 }
 
+- (void)dealloc {
+  [_flutterAccessibilityContainer release];
+  [super dealloc];
+}
+
 @end
 
 @implementation DelayingGestureRecognizer {

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -440,7 +440,7 @@ class FlutterPlatformViewsController {
 - (UIView*)embeddedView;
 
 // Sets flutterAccessibilityContainer as this view's accessibilityContainer.
-- (void)setFlutterAccessibilityContainer:(NSObject*)flutterAccessibilityContainer;
+@property(nonatomic, retain) id flutterAccessibilityContainer;
 @end
 
 @interface UIView (FirstResponder)

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

@@ -867,7 +867,7 @@ - (UIAccessibilityTraits)accessibilityTraits {
 @end
 
 @interface FlutterPlatformViewSemanticsContainer ()
-@property(nonatomic, retain) UIView* platformView;
+@property(nonatomic, assign) UIView* platformView;
 @end
 
 @implementation FlutterPlatformViewSemanticsContainer
@@ -876,14 +876,13 @@ - (instancetype)initWithBridge:(fml::WeakPtr<flutter::AccessibilityBridgeIos>)br
                            uid:(int32_t)uid
                   platformView:(nonnull FlutterTouchInterceptingView*)platformView {
   if (self = [super initWithBridge:bridge uid:uid]) {
-    _platformView = [platformView retain];
+    _platformView = platformView;
     [platformView setFlutterAccessibilityContainer:self];
   }
   return self;
 }
 
 - (void)dealloc {
-  [_platformView release];
   _platformView = nil;
   [super dealloc];
 }

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

@@ -994,19 +994,30 @@ - (void)testFlutterPlatformViewSemanticsContainer {
       new flutter::testing::MockAccessibilityBridge());
   fml::WeakPtr<flutter::testing::MockAccessibilityBridge> bridge = factory.GetWeakPtr();
   __weak FlutterTouchInterceptingView* weakPlatformView;
+  __weak FlutterPlatformViewSemanticsContainer* weakContainer;
   @autoreleasepool {
     FlutterTouchInterceptingView* platformView = [[FlutterTouchInterceptingView alloc] init];
     weakPlatformView = platformView;
-    FlutterPlatformViewSemanticsContainer* container =
-        [[FlutterPlatformViewSemanticsContainer alloc] initWithBridge:bridge
-                                                                  uid:1
-                                                         platformView:platformView];
-    XCTAssertEqualObjects(platformView.accessibilityContainer, container);
+
+    @autoreleasepool {
+      FlutterPlatformViewSemanticsContainer* container =
+          [[FlutterPlatformViewSemanticsContainer alloc] initWithBridge:bridge
+                                                                    uid:1
+                                                           platformView:platformView];
+      weakContainer = container;
+      XCTAssertEqualObjects(platformView.accessibilityContainer, container);
+      XCTAssertNotNil(weakPlatformView);
+      XCTAssertNotNil(weakContainer);
+    }
+    // Check the variables are still lived.
+    // `container` is `retain` in `platformView`, so it will not be nil here.
     XCTAssertNotNil(weakPlatformView);
+    XCTAssertNotNil(weakContainer);
   }
   // Check if there's no more strong references to `platformView` after container and platformView
   // are released.
   XCTAssertNil(weakPlatformView);
+  XCTAssertNil(weakContainer);
 }
 
 - (void)testTextInputSemanticsObject {