Summary:
Motivation:
* Current implementation of `didUpdateReactSubviews` relies on `processUpdatedProperties:parentProperties:` method of RCTShadowView, which we plan to remove.
* The existing implementation does not call handlers on unmounted nodes (because they are not part of traversing tree), which is not correct.
* The current implementation is tight with RCTComponentData, which is conceptually wrong, it should be a UIManager thing.
* The new implementation must be much more performant because of simplicity. (We can measure it only after removing `processUpdatedProperties`.)
Reviewed By: mmmulani
Differential Revision: D6595780
fbshipit-source-id: a517207c17b5d5db839c9ce99a37136292acf78c
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