* Implemented new getSnapshotBeforeUpdate lifecycle
* Store snapshot value from Fiber to instance (__reactInternalSnapshotBeforeUpdate)
* Use commitAllHostEffects() traversal for getSnapshotBeforeUpdate()
* Added DEV warnings and tests for new lifecycle
* Don't invoke legacy lifecycles if getSnapshotBeforeUpdate() is defined. DEV warn about this.
* Converted did-warn objects to Sets in ReactFiberClassComponent
* Replaced redundant new lifecycle checks in a few methods
* Check for polyfill suppress flag on cWU as well before warning
* Added Snapshot bit to HostEffectMask