Fix screen layout with non-translucent header on iOS. (#222)

After #184 we no longer were acconting for the size of navigation bar when laying out screens on the stack. This was causing elements to be drawn under a non-translucent bar unless SafeAreaView's been used. As this seem not to be desirable in most of the cases (there is no way of seeing items rendered underneath non-translucent header) this change brings back the previous behavior. Instead of using manual method of calculating top inset as it's been done before we rely on edgesForExtendedLayout property of the view controller.

ios/RNSScreenStackHeaderConfig.m

@@ -152,6 +152,15 @@
   BOOL wasHidden = navctr.navigationBarHidden;
   BOOL shouldHide = config == nil || config.hide;
 
+  if (!shouldHide && !config.translucent) {
+    // when nav bar is not translucent we chage edgesForExtendedLayout to avoid system laying out
+    // the screen underneath navigation controllers
+    vc.edgesForExtendedLayout = UIRectEdgeNone;
+  } else {
+    // system default is UIRectEdgeAll
+    vc.edgesForExtendedLayout = UIRectEdgeAll;
+  }
+
   [navctr setNavigationBarHidden:shouldHide animated:YES];
   navctr.interactivePopGestureRecognizer.enabled = config.gestureEnabled;
 #ifdef __IPHONE_13_0