## Summary

`fastAddProperties` has shown some perf benefits when used for creating
props payload for new components. In this PR we'll try to use it for
diffing props for existing components.

It would be good enough if it simply doesn't regress perf. We'll be able
to delete the old `addProperties`, and make `fastAddProperties` the
default behaviour.

## How did you test this change?

```
yarn lint
yarn flow native
yarn test packages/react-native-renderer -r=xplat --variant=false
yarn test packages/react-native-renderer -r=xplat --variant=true
```