Fix state.padding being out of sync with safe area view

Summary:
Changelog: [Internal]

# Problem

SafeAreaView is getting reused, its previous `safeAreaInsets` is top: 44, bottom: 34 so `safeAreaInsetsDidChange` doesn't get called because it doesn't change. Therefore state gets never updates because `safeAreaInsetsDidChange` is never called.

# Solution

Update state whenever a new state is assigned.

Reviewed By: shergin

Differential Revision: D20444198

fbshipit-source-id: 75d1458450c70d74647df4962ddad88d5f6a38d2

React/Fabric/Mounting/ComponentViews/SafeAreaView/RCTSafeAreaViewComponentView.mm

@@ -49,6 +49,11 @@ using namespace facebook::react;
 {
   [super safeAreaInsetsDidChange];
 
+  [self _updateStateIfNecessary];
+}
+
+- (void)_updateStateIfNecessary
+{
   if (!_state) {
     return;
   }
@@ -78,6 +83,7 @@ using namespace facebook::react;
            oldState:(facebook::react::State::Shared const &)oldState
 {
   _state = std::static_pointer_cast<SafeAreaViewShadowNode::ConcreteState const>(state);
+  [self _updateStateIfNecessary];
 }
 
 + (ComponentDescriptorProvider)componentDescriptorProvider