Janic Duplessis c47759a9ae Fix potential retain cycles in Animated iOS
Summary:
Fixes potential retain cycles detected by an internal fb tool.

```
First:

__NSDictionaryM
-> RCTPropsAnimatedNode
-> _parentNodes -> __NSDictionaryM
-> RCTStyleAnimatedNode
-> _childNodes -> __NSDictionaryM

Second:

RCTScrollView
-> _eventDispatcher -> RCTEventDispatcher
-> _observers -> __NSArrayM
-> RCTNativeAnimatedModule
-> _nodesManager -> RCTNativeAnimatedNodesManager
-> _uiManager -> RCTUIManager
-> _viewRegistry -> __NSDictionaryM
-> RCTScrollView
```

First fix:
Use weak map for parent and child nodes, strong refs are managed by RCTNativeAnimatedNodesManager

Second fix:
Make RCTEventDispatcher observers a weak array and make sure we don't keep strong refs to UIManager in RCTNativeAnimatedNodesManager and RCTPropsAnimatedNode.

Tested that native animations still work in UIExplorer

[IOS] [BUGFIX] [NativeAnimated] - Fix potential retain cycles in Animated iOS
Closes https://github.com/facebook/react-native/pull/16506

Differential Revision: D6126400

Pulled By: shergin

fbshipit-source-id: 1ac5083f8ab79a806305edc23ae4796ed428f78b
2017-10-23 13:20:59 -07:00
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