test/checkpoint: copy data using checkpoint cursor

(This was created as an output of WT-10638.)

test/checkpoint was identified as a good candidate for further testing of RTS, but there's some preliminary work to do first. This ticket is to get the infrastructure in place for comparing two tables after a rollback to stable, which would involve (1) adding a SIGSTOP handler and configuration option to test/checkpoint, and trigger writing a copy of all data using a checkpoint cursor.