Enable to activate Grain after clearing its state

[scalalang2]

resolve #9154

Background

The ClearStateAsync funcction doesn't remove the entry from storage by default.
Instead it only sets the state value to null,

If ReadStateAsync() is invoked when the value is null,
then it occurs an error from Serializer. Insufficient data present in buffer.

This error happens during the process of restarting our cluster.

1. The default value of DeleteStateOnClear is false.
2. The PubSubRendezvousGrain activates upon stream registration.
3. It calls ClearStateAsync() if there are no producers.
4. the grain reactivates after being deactivated, ReadStateAsync() is invoked
5. This leads to an error -> Insufficient data present in buffer.

Microsoft Reviewers: Open in CodeFlow

[ReubenBond]

@benjaminpetit PTAL