Pass layoutDirection to surface handler

Summary:
Changelog: [internal]

During transition to SurfaceHandler, layoutDirection got lost. This diff adds it back.

Reviewed By: JoshuaGross

Differential Revision: D26775873

fbshipit-source-id: 9b638b4c2a41eb887312b968a2e113c5fcd7463d

React/Fabric/Surface/RCTFabricSurface.mm

@@ -168,6 +168,8 @@ using namespace facebook::react;
 - (void)_updateLayoutContext
 {
   auto layoutConstraints = _surfaceHandler->getLayoutConstraints();
+  layoutConstraints.layoutDirection = RCTLayoutDirection([[RCTI18nUtil sharedInstance] isRTL]);
+
   auto layoutContext = _surfaceHandler->getLayoutContext();
 
   layoutContext.pointScaleFactor = RCTScreenScale();

ReactCommon/react/renderer/scheduler/SurfaceHandler.cpp

@@ -58,6 +58,9 @@ void SurfaceHandler::start() const noexcept {
     std::unique_lock<better::shared_mutex> lock(linkMutex_);
     react_native_assert(
         link_.status == Status::Registered && "Surface must be registered.");
+    react_native_assert(
+        getLayoutConstraints().layoutDirection != LayoutDirection::Undefined &&
+        "layoutDirection must be set.");
 
     auto parameters = Parameters{};
     {