Adds launch image for iPhone X and iPad to showSplashScreen. (#2321)

ios/RCCManager.m

         imageName = [imageName stringByAppendingString:@"-800-667h"];
       else if (screenHeight == 736)
         imageName = [imageName stringByAppendingString:@"-800-Portrait-736h"];
-      
+      else if (screenHeight == 812)
+        imageName = [imageName stringByAppendingString:@"-1100-Portrait-2436h"];
+      else if (screenHeight == 1024)
+        imageName = [imageName stringByAppendingString:@"-Portrait"];
+
       image = [UIImage imageNamed:imageName];
     }