Don't call sharedApplication in App Extension (#25769)

Summary:
Fixes #25767 .

## Changelog

[iOS] [Fixed] - Don't call sharedApplication in App Extension
Pull Request resolved: #25769

Test Plan: RN works in App Extension.

Reviewed By: cpojer

Differential Revision: D16516104

Pulled By: sammy-SC

fbshipit-source-id: 446fd1d88724b783b2afb2369783b9a85b5cc178

React/Modules/RCTRedBox.m

@@ -161,7 +161,7 @@ - (instancetype)initWithFrame:(CGRect)frame
 - (NSInteger)bottomSafeViewHeight
 {
     if (@available(iOS 11.0, *)) {
-        return [UIApplication sharedApplication].delegate.window.safeAreaInsets.bottom;
+        return RCTSharedApplication().delegate.window.safeAreaInsets.bottom;
     } else {
         return 0;
     }