[iOS] Fixes SplashScreenView crash when remove from view hierarchy

shell/platform/darwin/ios/framework/Headers/FlutterViewController.h

@@ -197,7 +197,7 @@ FLUTTER_DARWIN_EXPORT
 
 /**
  * Specifies the view to use as a splash screen. Flutter's rendering is asynchronous, so the first
- * frame rendered by the Flutter application might not immediately appear when theFlutter view is
+ * frame rendered by the Flutter application might not immediately appear when the Flutter view is
  * initially placed in the view hierarchy. The splash screen view will be used as
  * a replacement until the first frame is rendered.
  *

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

@@ -507,14 +507,15 @@ - (void)callViewRenderedCallback {
 
 - (void)removeSplashScreenView:(dispatch_block_t _Nullable)onComplete {
   NSAssert(_splashScreenView, @"The splash screen view must not be null");
-  UIView* splashScreen = _splashScreenView.get();
+  UIView* splashScreen = [_splashScreenView.get() retain];
   _splashScreenView.reset();
   [UIView animateWithDuration:0.2
       animations:^{
         splashScreen.alpha = 0;
       }
       completion:^(BOOL finished) {
         [splashScreen removeFromSuperview];
+        [splashScreen release];
         if (onComplete) {
           onComplete();
         }

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

@@ -433,6 +433,15 @@ - (void)testViewDidLoadDoesntInvokeEngineAttachViewWhenEngineNeedsLaunch {
   OCMVerify(never(), [mockEngine attachView]);
 }
 
+- (void)testSplashScreenViewRemoveNotCrash {
+  FlutterEngine* engine = [[FlutterEngine alloc] initWithName:@"engine" project:nil];
+  [engine runWithEntrypoint:nil];
+  FlutterViewController* flutterViewController =
+      [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
+  [flutterViewController setSplashScreenView:[[UIView alloc] init]];
+  [flutterViewController setSplashScreenView:nil];
+}
+
 - (void)testInternalPluginsWeakPtrNotCrash {
   FlutterSendKeyEvent sendEvent;
   @autoreleasepool {