[web][native] implement encrypting and persisting OutboundP2PMessage's content in the same SQLite transaction as persisting olm session

Summary:
To make sure the order is correct also on the sender's side we have to do it in exactly the same SQLite transaction.

A similar approach to decryptSequentialAndPersist.

Depends on D12080

Test Plan: Call this method and make sure data is persisted. Tested end-to-end in D12133.

Reviewers: tomek, marcin

Reviewed By: marcin

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12129