CR: annotate device constants

// FREEBIE

SignalMessaging/ViewControllers/OWSNavigationController.m

@@ -116,7 +116,9 @@ NS_ASSUME_NONNULL_BEGIN
         if (OWSWindowManager.sharedManager.hasCall) {
             if (UIDevice.currentDevice.isIPhoneX) {
                 // iPhoneX computes status bar height differently.
+                // IOS_DEVICE_CONSTANT
                 self.additionalSafeAreaInsets = UIEdgeInsetsMake(navbar.navbarWithoutStatusHeight + 20, 0, 0, 0);
+
             } else {
                 self.additionalSafeAreaInsets
                     = UIEdgeInsetsMake(navbar.navbarWithoutStatusHeight + CurrentAppContext().statusBarHeight, 0, 0, 0);

SignalMessaging/categories/UIDevice+featureSupport.swift

@@ -23,6 +23,7 @@ public extension UIDevice {
         case 2436:
             return true
         default:
+            // Verify all our IOS_DEVICE_CONSTANT tags make sense when adding a new device size.
             owsFail("\(logTag) in \(#function) unknown device format")
             return false
         }

SignalMessaging/utils/OWSWindowManager.m

@@ -19,8 +19,10 @@ const CGFloat OWSWindowManagerCallScreenHeight(void)
         // On an iPhoneX, the system return-to-call banner has been replaced by a much subtler green
         // circle behind the system clock. Instead, we mimic the old system call banner as on older devices,
         // but it has to be taller to fit beneath the notch.
+        // IOS_DEVICE_CONSTANT, we'll want to revisit this when new device dimensions are introduced.
         return 64;
     } else {
+
         return CurrentAppContext().statusBarHeight + 20;
     }
 }