Fix FlatList ItemSeparatorComponent type

[bigcupcoffee]

Summary

FlatList's ItemSeparatorComponent type did not support passing in react element as per documented in docs.

Changelog

[GENERAL] [FIXED] - Fix FlatList ItemSeparatorComponent type

Test Plan

None needed

[bigcupcoffee]

Welp from what I see in the code VirtualizedSectionList actually does not support react element as ItemSeparatorComponent, yet it's documented as supported? Do I make it support it or...

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	8,482,874	-2,842
android	hermes	armeabi-v7a	7,803,849	-2,674
android	hermes	x86	8,959,792	-3,102
android	hermes	x86_64	8,817,172	-2,728
android	jsc	arm64-v8a	9,116,966	+2,417,516
android	jsc	armeabi-v7a	8,313,038	+822,057
android	jsc	x86	9,168,369	-55,664
android	jsc	x86_64	9,427,203	+2,502,537

Base commit: cb28a2c
Branch: main

[NickGerleman]

Welp from what I see in the code VirtualizedSectionList actually does not support react element as ItemSeparatorComponent, yet it's documented as supported? Do I make it support it or...

Does it work for FlatList, but not VirtualizedSectionList? It is does work for FlatList, but only FlatList, we could put this in FlatList typings instead of VirtualizedList typings.

[bigcupcoffee]

@NickGerleman I believe problem is VirtualizedSectionList does not properly override VirtualizedList's ItemSeparatorComponent type, and thus this.props.ItemSeparatorComponent comes in as possible Element which it should not be according to both code and the type override attempt (probably not I'm just very lost in all the code atm) here. Worth noting that SectionList docs actually state Element is supported as well, so we either support element in section list, or fix the type override and edit docs?

[bigcupcoffee]

@NickGerleman hey, would this get any attention? I'm glad to modify the PR as long as I know what would be the best fit here

[yungsters]

Thanks for the contribution, @bigcupcoffee!

It looks like support for elements was added in #32748.

However, there are Flow type errors surfaced by Circle CI. Can you look into fixing those? I can merge this after the errors addressed.

[yungsters]

Also, I apologize for the delay in reviewing this. (For some reason, our internal tooling that helps surface PRs was not working correctly.)

[yungsters]

Requesting changes due to Flow errors in Circle CI.

[bigcupcoffee]

@yungsters I'm not sure how to fix the SectionList flow error, there seems to be an override already here, which should mark the prop as Component only (since VirtualizedSectionList due to its own separator implementation doesn't support Element as for now, this code). I guess it comes from the info.section.ItemSeparatorComponent || this.props.ItemSeparatorComponent and one of these end up having Element as a possible type. I'm not good with flow so not sure how to resolve that, would really use some help here. While for VirtualizedList error, if I'm correct, you just need to add support for React.Element right here and that should fix it.

Awaiting your reply about SectionList, as once again, docs state that Element is supported, so that should be fixed too?

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