fix: Initial animated style updater style is applied on re-render

[MatiPl01]

Summary

This PR fixes #7375.

The problem

After removing style flattening the old implementation started being invalid because the _initialStyle object that was created during the initial render of the component contained props from all animated styles. If a view had more than just one animated style, this object contained props from all of these styles.

Let's say we had these 3 animated styles:

const aStyle1 = useAnimatedStyle(() => ({})); // empty

const aStyle2 = useAnimatedStyle(() => ({
  height: 100
}));

const aStyle3 = useAnimatedStyle(() => ({
  width: 100
}));

<Animated.View style={[aStyle1, aStyle2, aStyle3]} />

The style array on the first render looked like this:

[{}, { height: 100 }, { height: 100, width: 100 }] // subsequent objects contain all props from previous objects because of merging

On the next render, however, the _initialStyle was used for all animated styles, so we ended up with this array:

[{ height: 100, width: 100 }, { height: 100, width: 100 }, { height: 100, width: 100 }]

As a result, 2 of 3 styles changed. Because the implementation is different on Paper and we have no props registry (similar to what we have on Fabric), this change resulted in the view's style update, even though the animated style wasn't recalculated and didn't return a new style. This is an incorrect behavior resulting in problems described in the attached issue.

The solution

I decided to create a map with style objects and their initial run values. As a result, instead of returning the same single style object with all style props from all animated styles, we can now return proper initial style values for a specific animated style.

Test plan

Copy the example from #7375 issue and see that it now works.

[MatiPl01]

I tested this solution on a few examples on Paper and Fabric. It seems to work on both but there was no issue on Fabric so I wonder if we want to merge it on the main branch as well.

[tomekzaw]

LGTM

[efstathiosntonas]

thank you fellas!! ❤️❤️

[efstathiosntonas]

I think this should be released asap, it was really tricky in my case to find out that reanimated was the cause and possibly many packages or daily coding could be affected!

[MatiPl01]

I think this should be released asap, it was really tricky in my case to find out that reanimated was the cause and possibly many packages or daily coding could be affected!

We will release a new version at the beginning of the next week. For now, you can patch reanimated.