In banner view, pin top elements to the bottom of the status bar (#5100)

* Add constraint to pin title label below status bar in banner FIAM

* Remove title label top pin from storyboard at build time

* Use conditional compilation for iOS 13 check

Author: christibbs

FirebaseInAppMessaging/Resources/FIRInAppMessageDisplayStoryboard.storyboard

@@ -95,7 +95,7 @@
                             </constraint>
                             <constraint firstItem="GOK-vx-mU8" firstAttribute="leading" secondItem="rzo-9i-rXZ" secondAttribute="leading" id="J6L-hu-jV6"/>
                             <constraint firstItem="VfB-vw-7up" firstAttribute="leading" secondItem="vRb-yf-OWE" secondAttribute="leading" constant="5" id="gGt-ku-pPu"/>
-                            <constraint firstItem="rzo-9i-rXZ" firstAttribute="top" secondItem="lHf-Ux-dEc" secondAttribute="bottom" constant="3" id="hhi-1K-2YO"/>
+                            <constraint firstItem="rzo-9i-rXZ" firstAttribute="top" secondItem="lHf-Ux-dEc" secondAttribute="bottom" constant="3" placeholder="YES" id="hhi-1K-2YO"/>
                             <constraint firstItem="VfB-vw-7up" firstAttribute="top" secondItem="rzo-9i-rXZ" secondAttribute="top" id="nF9-EZ-bjS"/>
                             <constraint firstAttribute="trailingMargin" secondItem="rzo-9i-rXZ" secondAttribute="trailing" id="pOl-wC-mqq"/>
                             <constraint firstItem="rzo-9i-rXZ" firstAttribute="leading" secondItem="VfB-vw-7up" secondAttribute="trailing" constant="5" id="vSo-6t-cZ0"/>

FirebaseInAppMessaging/Sources/DefaultUI/Banner/FIRIAMBannerViewController.m

@@ -155,6 +155,25 @@ - (void)viewDidLoad {
   self.view.layer.shadowRadius = 2;
   self.view.layer.shadowOpacity = 0.4;
 
+  // Calculate status bar height.
+  CGFloat statusBarHeight = 0;
+#if defined(__IPHONE_13_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000
+  if (@available(iOS 13.0, *)) {
+    UIStatusBarManager *manager =
+        [UIApplication sharedApplication].keyWindow.windowScene.statusBarManager;
+
+    statusBarHeight = manager.statusBarFrame.size.height;
+  } else {
+#endif
+    statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height;
+#if defined(__IPHONE_13_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000
+  }
+#endif
+
+  // Pin title label below status bar with cushion.
+  [[self.titleLabel.topAnchor constraintEqualToAnchor:self.view.topAnchor
+                                             constant:statusBarHeight + 3] setActive:YES];
+
   // When created, we are hiding it for later animation
   self.hidingForAnimation = YES;
   [self setupAutoDismissTimer];