Demonstrate bug in differentiator where reparented nodes reference no…

…n-existent nodes (#48002)

Summary:
Pull Request resolved: #48002

Demonstrates the issue identified in #47960 and a crash we've been seeing internally around `getViewState` referencing a view that does not exist.

When reparenting unflattened nodes, Differentiator may emit an `update` with a `parentShadowView` that does not exist on the native side yet, thereby crashing Android.

Landing the test-case first (with some test cleanup), so the diff for the actual fix is clearer.

Changelog: [Internal]

Reviewed By: lenaic

Differential Revision: D66557919

fbshipit-source-id: 5428c32e5f0200a8e98568cabeedb0c61aafbe23