When a backup is taken on a database we should check that the database being backed up is not in the middle of a live restore. If it is the files contains holes and are missing data.

This ticket has two components:

1) Add a validity check that backup will fail when taking a backup of a directory that is in the process of being live restored. To do this we can check for stop files or for a state file that is not in the WTI_LIVE_RESTORE_STATE_COMPLETE state

2) If there is a WiredTigerLR.state file in the COMPLETE state (and no other stop files exist) Backup should delete this file before taking a snapshot.