[iOS API breaking change] Make splashScreenView of FlutterViewController nullable (flutter#34743)

Author: zhongwuzw

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

@@ -203,8 +203,10 @@ FLUTTER_DARWIN_EXPORT
  *
  * The view used should be appropriate for multiple sizes; an autoresizing mask to
  * have a flexible width and height will be applied automatically.
+ *
+ * Set to nil to remove the splash screen view.
  */
-@property(strong, nonatomic) UIView* splashScreenView;
+@property(strong, nonatomic, nullable) UIView* splashScreenView;
 
 /**
  * Attempts to set the `splashScreenView` property from the `UILaunchStoryboardName` from the

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

@@ -1135,4 +1135,11 @@ - (void)testFakeEventTimeStamp {
   XCTAssertTrue(interval_micros / 1000 < tolerance_millis,
                 @"PointerData.time_stamp should be equal to NSProcessInfo.systemUptime");
 }
+
+- (void)testSplashScreenViewCanSetNil {
+  FlutterViewController* flutterViewController =
+      [[FlutterViewController alloc] initWithProject:nil nibName:nil bundle:nil];
+  [flutterViewController setSplashScreenView:nil];
+}
+
 @end