Add support for prefersLargeTitles in iOS 11 (#2593)

docs/styling-the-navigator.md

   preferredContentSize: { width: 500, height: 500 } // Sets the preferred size for the view controller’s view.
   modalPresentationStyle: 'formSheet' // Sets the presentation style for modally presented view controllers. Supported styles are: 'formSheet', 'pageSheet', 'overFullScreen', 'overCurrentContext' and 'fullScreen'. 
   
+  largeTitle: false, // Sets the nav bar title to be in the larger iOS 11 style
+
   // Android only
   navigationBarColor: '#000000', // change the background color of the bottom native navigation bar.
   navBarTitleTextCentered: true, // default: false. centers the title.

ios/RCCViewController.m

       self.navigationItem.titleView.clipsToBounds = YES;
     }
   }
+
+  if (@available(iOS 11.0, *)) {
+    if ([self.navigationController.navigationBar respondsToSelector:@selector(setPrefersLargeTitles:)]) {
+      NSNumber *prefersLargeTitles = self.navigatorStyle[@"largeTitle"];
+      if (prefersLargeTitles) {
+        if ([prefersLargeTitles boolValue]) {
+          self.navigationController.navigationBar.prefersLargeTitles = YES;
+          self.navigationItem.largeTitleDisplayMode = UINavigationItemLargeTitleDisplayModeAlways;
+        } else {
+          self.navigationItem.largeTitleDisplayMode = UINavigationItemLargeTitleDisplayModeNever;
+        }
+      } else {
+        self.navigationController.navigationBar.prefersLargeTitles = NO;
+        self.navigationItem.largeTitleDisplayMode = UINavigationItemLargeTitleDisplayModeNever;
+      }
+    }
+  }
 }