Summary:
`flattenOffset` has proven extremely useful, especially when dealing with pan responders and other gesture based animations, but I've also found a number of use cases for the inverse. This diff introduces `extractOffset`, which sets the offset value to the base value, and resets the base value to zero. A common use case would be to extractOffset onGrant and flattenOffset onRelease.
Closes https://github.com/facebook/react-native/pull/10721
Differential Revision: D4145744
fbshipit-source-id: dc2aa31652df0b31450556f611db43548180c7dd
6535858c71