fix build issue by moving flutterScreenIfViewLoaded

Author: hellohuanlin

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

@@ -164,4 +164,13 @@ FLUTTER_DARWIN_EXPORT
 - (instancetype)initWithOwner:(FlutterTextInputPlugin*)textInputPlugin NS_DESIGNATED_INITIALIZER;
 
 @end
+
+@interface UIViewController (FlutterScreenAndSceneIfLoaded)
+
+/// Before iOS 13, returns the main screen; After iOS 13, returns the screen the UIViewController is
+/// attached to if its view is loaded, and nil otherwise.
+- (UIScreen*)flutterScreenIfViewLoaded;
+
+@end
+
 #endif  // SHELL_PLATFORM_IOS_FRAMEWORK_SOURCE_FLUTTERTEXTINPUTPLUGIN_H_

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

@@ -2762,3 +2762,26 @@ - (BOOL)handlePress:(nonnull FlutterUIPressProxy*)press API_AVAILABLE(ios(13.4))
   return NO;
 }
 @end
+
+@implementation UIViewController (FlutterScreenAndSceneIfLoaded)
+
+- (UIWindowScene*)flutterWindowSceneIfViewLoaded {
+  if (self.viewIfLoaded == nil) {
+    FML_LOG(WARNING) << "Trying to access the window scene before the view is loaded.";
+    return nil;
+  }
+  return self.viewIfLoaded.window.windowScene;
+}
+
+- (UIScreen*)flutterScreenIfViewLoaded {
+  if (@available(iOS 13.0, *)) {
+    if (self.viewIfLoaded == nil) {
+      FML_LOG(WARNING) << "Trying to access the screen before the view is loaded.";
+      return nil;
+    }
+    return [self flutterWindowSceneIfViewLoaded].screen;
+  }
+  return UIScreen.mainScreen;
+}
+
+@end