Fix ItemSeparatorComponent's leadingItem prop not being updated (#25114)
Fix ItemSeparatorComponent's leadingItem prop not being updated (#25114)

Summary:
Fix https://github.com/facebook/react-native/issues/24592

Just added a `getDerivedStateFromProps`, similar to what `VirtualizedSectionList` already does: https://github.com/facebook/react-native/blob/18fededae085b53b01e54a7ed27e32c2318e7cae/Libraries/Lists/VirtualizedSectionList.js#L470-L492

## Changelog

[General] [Fixed] - Fix ItemSeparatorComponent's leadingItem prop not being updated
Pull Request resolved: https://github.com/facebook/react-native/pull/25114

Differential Revision: D15602460

Pulled By: cpojer

fbshipit-source-id: b16a82912fd746a956f6aa360d18ade53357f634

myntra/react-native,exponentjs/react-native,javache/react-native,myntra/react-native,facebook/react-native,facebook/react-native,hoangpham95/react-native,hoangpham95/react-native,janicduplessis/react-native,facebook/react-native,exponent/react-native,javache/react-native,myntra/react-native,javache/react-native,hammerandchisel/react-native,pandiaraj44/react-native,janicduplessis/react-native,exponentjs/react-native,exponent/react-native,facebook/react-native,hoangpham95/react-native,facebook/react-native,javache/react-native,hammerandchisel/react-native,hammerandchisel/react-native,exponent/react-native,hoangpham95/react-native,janicduplessis/react-native,exponentjs/react-native,janicduplessis/react-native,javache/react-native,arthuralee/react-native,hammerandchisel/react-native,myntra/react-native,exponentjs/react-native,myntra/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,hoangpham95/react-native,pandiaraj44/react-native,arthuralee/react-native,arthuralee/react-native,javache/react-native,facebook/react-native,facebook/react-native,facebook/react-native,exponentjs/react-native,exponentjs/react-native,janicduplessis/react-native,hammerandchisel/react-native,hoangpham95/react-native,janicduplessis/react-native,myntra/react-native,hammerandchisel/react-native,exponentjs/react-native,exponent/react-native,pandiaraj44/react-native,hammerandchisel/react-native,myntra/react-native,pandiaraj44/react-native,exponent/react-native,arthuralee/react-native,janicduplessis/react-native,hammerandchisel/react-native,pandiaraj44/react-native,exponent/react-native,hoangpham95/react-native,myntra/react-native,exponent/react-native,javache/react-native,myntra/react-native,exponentjs/react-native,javache/react-native,janicduplessis/react-native,exponent/react-native,arthuralee/react-native,javache/react-native,hoangpham95/react-native,pandiaraj44/react-native