Migrate FlatList to FlashList

[muttmuure]

Problem

While FlatList is suitable for typical use cases, our goal is to achieve the highest level of app performance, especially when dealing with extensive lists, such as Chats, Threads, Workspaces, Reports, and specific Money Threads.

Chats list items have 3 dependant onyx queries, which needs to be fetched when new items are rendered (+ will cause 3 react renders)

Solution

To address this performance challenge, we propose switching from FlatList to FlashList. By making this transition, we anticipate a significant performance improvement of approximately 2x. The best part is that this solution is cross-platform compatible and requires minimal changes, primarily by utilizing the estimatedItemSize property.

[muttmuure]

Closing in favor of #28902