Shadow refactoring and improvements (#1959)

* Make shadow a type-only concept

* Prevent unnecessary init state recalc

* Use derived state instead of effects

* Batch emitter updates

* Use object first seen time instead of dataUpdatedAt

* Stop threading dataUpdatedAt through

* Use same value consistently

src/lib/batchedUpdates.ts

@@ -0,0 +1 @@
+export {unstable_batchedUpdates as batchedUpdates} from 'react-native'

src/lib/batchedUpdates.web.ts

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+// @ts-ignore
+export {unstable_batchedUpdates as batchedUpdates} from 'react-dom'