Prevent modal dismissal with swipe gestures

Summary:
(Fixing the problems in this diff https://our.intern.facebook.com/intern/diff/D19836548/)

iOS 13 introduced interactive dismissal for modals https://medium.com/hacknicity/view-controller-presentation-changes-in-ios-13-ac8c901ebc4e.
This breaks react modals. We're disabling this feature for react modals
Changelog: [iOS][Fixed]  Prevent interactive dismissal for non-fullscreen modals

Reviewed By: shergin

Differential Revision: D19880343

fbshipit-source-id: e2ad82db3dd827812824862f432d549c865216b9

React/Views/RCTModalHostViewController.m

@@ -25,6 +25,13 @@ - (instancetype)init
     return nil;
   }
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_13_0) && \
+__IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_13_0
+  if (@available(iOS 13.0, *)) {
+    self.modalInPresentation = YES;
+  }
+#endif
+
 #if !TARGET_OS_TV
   _preferredStatusBarStyle = [RCTSharedApplication() statusBarStyle];
   _preferredStatusBarHidden = [RCTSharedApplication() isStatusBarHidden];