Fix crash on macos when using Layout Animations (#6600)

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## Summary
Previously we were passing a window to function convertPoint, that
accepts only view. It was causing a crash, therefore we should pass the
contentView of the window.
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applicable. -->

## Test plan
Tested on several examples:
* Olympic example
* [LA] Basic Layout Animation
* [LA] Entering and Exiting with Layout 
* [LA] Carousel
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packages/react-native-reanimated/apple/reanimated/LayoutReanimation/REASnapshot.m

@@ -39,7 +39,7 @@ - (void)makeSnapshotForView:(REAUIView *)view
                 withOffsetY:(double)offsetY
 {
 #if TARGET_OS_OSX
-  REAUIView *mainWindow = UIApplication.sharedApplication.keyWindow;
+  NSView *mainWindow = UIApplication.sharedApplication.keyWindow.contentView;
 #else
   REAUIView *mainWindow = RCTKeyWindow();
 #endif