feat(iOS) remove deprecated [UIScreen mainScreen] references (faceboo…

…k#41388)

Summary:
The goal for this PR is to further remove references for `[UIScreen mainScreen]` and migrate them to use trait collections. This helps out of tree platforms like visionOS (where the `UIScreen` is not available).

bypass-github-export-checks

[INTERNAL] [CHANGED] - use currentTraitCollection for FBSnapshotTestController.m
[IOS] [CHANGED] - use key window width to assign the correct width for RCTDevLoadingView

Pull Request resolved: facebook#41388

Test Plan:
– Check if tests passes
- Check if `RCTDevLoadingView` shows up correctly.

Screenshot:
![CleanShot 2023-11-09 at 13 48 48@2x](https://github.com/facebook/react-native/assets/52801365/4c91399e-f70a-4e78-8288-bc7b8377c980)

Reviewed By: javache

Differential Revision: D51156230

Pulled By: cipolleschi

fbshipit-source-id: bbe711e0281046a082fd1680b55e2d117915ad00

packages/react-native/React/CoreModules/RCTDevLoadingView.mm

@@ -141,13 +141,11 @@ - (void)showMessage:(NSString *)message color:(RCTUIColor *)color backgroundColo
     self->_showDate = [NSDate date];
     if (!self->_window && !RCTRunningInTestEnvironment()) {
 #if !TARGET_OS_OSX // [macOS]
-      CGSize screenSize = [UIScreen mainScreen].bounds.size;
-
       UIWindow *window = RCTSharedApplication().keyWindow;
-      self->_window =
-          [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, screenSize.width, window.safeAreaInsets.top + 10)];
-      self->_label =
-          [[UILabel alloc] initWithFrame:CGRectMake(0, window.safeAreaInsets.top - 10, screenSize.width, 20)];
+      CGFloat windowWidth = window.bounds.size.width;
+
+      self->_window = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, windowWidth, window.safeAreaInsets.top + 10)];
+      self->_label = [[UILabel alloc] initWithFrame:CGRectMake(0, window.safeAreaInsets.top - 10, windowWidth, 20)];
       [self->_window addSubview:self->_label];
 
       self->_window.windowLevel = UIWindowLevelStatusBar + 1;

packages/rn-tester/RCTTest/FBSnapshotTestCase/FBSnapshotTestController.m

@@ -240,14 +240,15 @@ - (NSString *)_fileNameForSelector:(SEL)selector
   if (0 < identifier.length) {
     fileName = [fileName stringByAppendingFormat:@"_%@", identifier];
   }
-  CGFloat scale; // [macOS
-#if !TARGET_OS_OSX
-  scale = [[UIScreen mainScreen] scale];
-#else
+#if !TARGET_OS_OSX // [macOS]
+  UITraitCollection *currentTraitCollection = [UITraitCollection currentTraitCollection];
+  if (currentTraitCollection.displayScale > 1.0) {
+    fileName = [fileName stringByAppendingFormat:@"@%.fx", currentTraitCollection.displayScale];
+#else // [macOS
   scale = [[NSScreen mainScreen] backingScaleFactor];
-#endif
-  if (scale > 1.0) { // macOS]
+  if (scale > 1.0) {
     fileName = [fileName stringByAppendingFormat:@"@%.fx", scale];
+#endif // macOS]
   }
   fileName = [fileName stringByAppendingPathExtension:@"png"];
   return fileName;