Builds upon the `CellRenderMask` data structure added with facebook#31420, and VirtualizedList coverage added with facebook#31401.

VirtualizedList currently keeps a [first, last] range as state, tracking the region of cells to render. The render functions uses this as an input, along with a few special cases to render more (sticky headers, initial render region.)

This change moves to instead keep state which describes discontiguous render regions. This mask is continually updated as the viewport changes, batch renders expand the region, etc. Special cases are baked into the render mask, with a relatively simple tranformation from the mask to render function.

This representation makes it much easier to support keyboarding scenarios, which require keeping distinct regions (e.g. for last focused) realized while out of viewport.

MS/FB folks have a video discussion about VirtualizedList here: https://msit.microsoftstream.com/video/fe01a1ff-0400-94b1-d4f1-f1eb924b1809

facebook#31401 added quite a few snapshot tests, centering around the logic this change is touching. I manually validated RNTester FlatList examples (and their should be some upstream UI testing for them).