Remove unwanted animations

Summary:
Changelog: [internal]

# Problem
Assigning `CALayer.contents` implicitly animates the difference. As we keep `UIView` in recycle pool between usages, they keep their previous state. This was causing animation of border when the views were being reused.

# Solution
Wrapping application of mutations in `CATTransaction`.

Reviewed By: shergin

Differential Revision: D20442045

fbshipit-source-id: 214d6c422f23f399dec46b5bf1a38a7b64758160

React/Fabric/Mounting/RCTMountingManager.mm

@@ -135,6 +135,8 @@ static void RNPerformMountInstructions(
 {
   SystraceSection s("RNPerformMountInstructions");
 
+  [CATransaction begin];
+  [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
   for (auto const &mutation : mutations) {
     switch (mutation.type) {
       case ShadowViewMutation::Create: {
@@ -189,6 +191,7 @@ static void RNPerformMountInstructions(
       }
     }
   }
+  [CATransaction commit];
 }
 
 @implementation RCTMountingManager {