Update DevLoadingView to Support iPhone X

Summary:
The current implementation of DevLoadingView for iPhone currently gives a static height of `22` and does not take into account iPhoneX screen dimensions.

Devices: All iPhone devices currently available with Xcode v9.2
SDK: 8.1, 9, 10, 11

Validate resize only occurs on iPhone X devices and others remain consistent.

Before:
![feb-10-2018 12-30-20](https://user-images.githubusercontent.com/1743953/36065313-7b41f2ea-0e5e-11e8-87f2-928e26536077.gif)

After:
![feb-10-2018 12-28-15](https://user-images.githubusercontent.com/1743953/36065317-848e4f7e-0e5e-11e8-8aab-70cb5db32f31.gif)

[GENERAL][ENHANCEMENT][{React}] - Improvements to DevLoadingView for iPhone X
Closes #17936

Differential Revision: D6962962

Pulled By: shergin

fbshipit-source-id: e11d9386544fe19a9195e22a03e12f64e934cad7

Author: mrtnrst

React/DevSupport/RCTDevLoadingView.m

@@ -73,8 +73,15 @@ - (void)setBridge:(RCTBridge *)bridge
   dispatch_async(dispatch_get_main_queue(), ^{
     self->_showDate = [NSDate date];
     if (!self->_window && !RCTRunningInTestEnvironment()) {
-      CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
-      self->_window = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, screenWidth, 22)];
+      CGSize screenSize = [UIScreen mainScreen].bounds.size;
+      if (screenSize.height == 812 /* iPhone X */) {
+        self->_window = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, screenSize.width, 60)];
+        self->_label = [[UILabel alloc] initWithFrame:CGRectMake(0, 30, self->_window.bounds.size.width, 30)];
+      } else {
+        self->_window = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, screenSize.width, 22)];
+        self->_label = [[UILabel alloc] initWithFrame:self->_window.bounds];
+      }
+      [self->_window addSubview:self->_label];
 #if TARGET_OS_TV
       self->_window.windowLevel = UIWindowLevelNormal + 1;
 #else
@@ -83,11 +90,8 @@ - (void)setBridge:(RCTBridge *)bridge
       // set a root VC so rotation is supported
       self->_window.rootViewController = [UIViewController new];
 
-      self->_label = [[UILabel alloc] initWithFrame:self->_window.bounds];
       self->_label.font = [UIFont systemFontOfSize:12.0];
       self->_label.textAlignment = NSTextAlignmentCenter;
-
-      [self->_window addSubview:self->_label];
     }
 
     self->_label.text = message;