Summary:
Adds some imperative VirtualizedList methods to the TS types which are documented on the website and are public enough. Also explicitly add `viewOffset` to `scrollToItem` since `scrollToItem` params are indefinite in flow and are passed to `scrollToIndex` (which supports the prop).
Changelog:
[General][Fixed] - Add missing VirtualizedList Imperative Types
Reviewed By: GijsWeterings
Differential Revision: D42047674
fbshipit-source-id: 60f7b35b049853d9fcb724918b3a0008a75ea573