pcr: prevent resuming replication after flashback

An `ALTER REVERT` will destroy the MVCC history back to the revert time which can cause physical replication to be incorrect.

If REVERT is run on the source for replication, we need to ensure that resumed replication resumes from the time reverted to, or previous divergence time, whichever is earlier. This means that that the source needs to send the revert time in the prior replication status call so that that can be used instead of the cutover time in the consumer's tenant record if it is earlier.

If REVERT is run on the consumer after cutover to a time earlier than the cutover time, it should haul backwards the tracked cover time to reflect the lost history.

Jira issue: CRDB-36893