fix: nested scroll in inverted VirtualizedList

[roryabraham]

Fixes #2435

Details

This workaround fixes wheel events in inverted FlatLists, but overrides the default wheel event handler for inputs. Therefore, if you have a scrollable node as a child of an inverted FlatList, the scroll on that node is broken unless you employ a workaround by adding a wheel event listener to the child as well.

This PR fixes the workaround for wheel events in inverted FlatList by:

1. Calculate the scroll for the event target (if any)
2. Calculate the "leftover scroll" in excess of the target scroll bounds (if any)
3. Applies the inverse of the "leftover scroll" on the FlatList

Testing steps

My testing steps were a bit crude...

1. Go to the codesandbox reproduction for the original issue
2. Observe the issue in action.
3. Open the JS console, and do a global search for invertedWheelEventHandler
4. Copy/paste this code change into the source code, removing the couple flow type annotations are in this function.
5. Observe the fix in action

[codesandbox-ci]

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Latest deployment of this branch, based on commit 8ca5167:

Sandbox	Source
react-native-web-examples	Configuration
RNW-NestedTextInputScroll	Issue #2435