RN: Further Optimize createAnimatedComponent

Summary:
In addition to memoizing `mergedStyle` in `createAnimatedComponent`, this avoids unnecessary object allocations by:

* Not allocating `passthroughProps`, created via a rest spread operator. It is unnecessary because we always override `style` in the JSX.
* Not allocating a new object if either `style` or `passthroughStyle` are null or undefined. Also, create an array of the two style objects instead of spreading them, which is needless.

Changelog:
[General][Changed] - Improved  performance of `Animated` components

Reviewed By: sammy-SC

Differential Revision: D56621191

fbshipit-source-id: ac863661c60d87c681284ce5ef5d6774b9c50653

Author: yungsters

packages/react-native/Libraries/Animated/createAnimatedComponent.js

@@ -8,6 +8,7 @@
  * @format
  */
 
+import composeStyles from '../../src/private/core/composeStyles';
 import View from '../Components/View/View';
 import useMergeRefs from '../Utilities/useMergeRefs';
 import useAnimatedProps from './useAnimatedProps';
@@ -45,17 +46,18 @@ export default function createAnimatedComponent<TProps: {...}, TInstance>(
       // without these passthrough values.
       // $FlowFixMe[prop-missing]
       const {passthroughAnimatedPropExplicitValues, style} = reducedProps;
-      const {style: passthroughStyle, ...passthroughProps} =
-        passthroughAnimatedPropExplicitValues ?? {};
+      const passthroughStyle = passthroughAnimatedPropExplicitValues?.style;
       const mergedStyle = useMemo(
-        () => ({...style, ...passthroughStyle}),
-        [style, passthroughStyle],
+        () => composeStyles(style, passthroughStyle),
+        [passthroughStyle, style],
       );
 
+      // NOTE: It is important that `passthroughAnimatedPropExplicitValues` is
+      // spread after `reducedProps` but before `style`.
       return (
         <Component
           {...reducedProps}
-          {...passthroughProps}
+          {...passthroughAnimatedPropExplicitValues}
           style={mergedStyle}
           ref={ref}
         />