Summary:
## Problem
When self is nil, this may crash in RCTUIImageViewAnimated.m.
```
_displayLink = [CADisplayLink displayLinkWithTarget:[RCTWeakProxy weakProxyWithTarget:self] selector:selector(displayDidRefresh:)];
```
## Fix
Replace `RCTWeakProxy` with a concrete class `RCTDisplayWeakRefreshable` that has the displayDidRefresh method, that calls the displayDidRefresh method in its weak target.
### Original Github Issue
https://github.com/facebook/react-native/pull/28070#issuecomment-619295254
Changelog: [iOS] [Fixed] - Fix Animated image crash when CADisplayLink target in RCTWeakProxy is nil
Reviewed By: shergin
Differential Revision: D21419385
fbshipit-source-id: da7c3c38f81ea54f633da7f59359e07680ea2faf
Paige Sun