Implement FeedFeedback API (#3498)

* Implement onViewableItemsChanged on List.web.tsx

* Introduce onItemSeen to List API

* Add FeedFeedback tracker

* Add clickthrough interaction tracking

* Add engagement interaction tracking

* Reduce duplicate sends, introduce a flushAndReset to be triggered on refreshes, and modify the api design a bit

* Wire up SDK types and feedContext

* Avoid needless function allocations

* Fix schema usage

* Add show more / show less buttons

* Fix minor rendering issue on mobile menu

* Wire up sendInteractions()

* Fix logic error

* Fix: it's item not uri

* Update 'seen' to mean 3 seconds on-screen with some significant portion visible

* Fix non-reactive debounce

* Move methods out

* Use a WeakSet for deduping

* Reset timeout

* 3 -> 2 seconds

* Oopsie

* Throttle instead

* Fix divider

* Remove explicit flush calls

* Rm unused

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Co-authored-by: dan <dan.abramov@gmail.com>

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