As part of WT-18194 we changed how data is encoded in the stable constituent of layered tables. Moving from escape encoding tombstones, to just writing user data directly.

The escape encoding was applied to be consistent with the format in the ingest file, but isn't necessary for the stable table- since deletes are directly applied, no tombstones are used.

The intent of this ticket is to leave a marker or schedule work to remove support for reading and writing escape-encoded tombstones a reasonable amount of time after all data has migrated to the new format. WiredTiger should be changed to fail to start with an obvious error message if tombstone-encoded data format is encountered after this change has been made.