Fabric: Fixing incorrect retaining policy for RCTSurfacePreseter (crash in RCTNativeAnimatedModule)

Summary:
This fixing a crash in RCTNativeAnimatedModule caused by accessing an `RCTSurfacePreseter` instance as "Objective-C runtime associated object" which was retained with `OBJC_ASSOCIATION_ASSIGN` policy. The documentation for `OBJC_ASSOCIATION_ASSIGN` says "Specifies a weak reference to the associated object." but it's a lie ( https://stackoverflow.com/questions/16569840/using-objc-setassociatedobject-with-weak-references) ). The policy is actually `ASSIGN` (aka `unsafe-unretained`).
That's why it's crashing.

We change that to `OBJC_ASSOCIATION_RETAIN` to retain the object (which meets the expectation of the interface of the category).

We also should not have over-retaining issues because:
* SurfacePresenter does not retain a Bridge or any object that can retain a Bridge;
* SurfacePresenter is a long-living object, we don't recreate it during bridge reloading or stuff like that.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D19333869

fbshipit-source-id: 1ff03659a880f2742b909c5668c47144719eeee2

React/Modules/RCTSurfacePresenterStub.m

@@ -16,7 +16,7 @@
 
 - (void)setSurfacePresenter:(id<RCTSurfacePresenterStub>)surfacePresenter
 {
-  objc_setAssociatedObject(self, @selector(surfacePresenter), surfacePresenter, OBJC_ASSOCIATION_ASSIGN);
+  objc_setAssociatedObject(self, @selector(surfacePresenter), surfacePresenter, OBJC_ASSOCIATION_RETAIN);
 }
 
 @end