dillon1000/react

Fix useMutableSource tearing bug (#18912)

* Failing useMutableSource test

If a source is mutated after initial read but before subscription is set
up, it should still entangle all pending mutations even if snapshot of
new subscription happens to match.

Test case illustrates how not doing this can lead to tearing.

* Fix useMutableSource tearing bug

Fix is to move the entanglement call outside of the block that checks
if the snapshot has changed.