After WT-17355, we can use the new WT_PAGE_LOG::pl_get_complete_checkpoint function from the PALI API to ensure that WiredTiger is on the latest completed checkpoint when stepping up, as this is an issue of correctness. We should perform this check in both diagnostic and release modes, so this should be an actual check that returns an error code (e.g., EINVAL) and logs the corresponding error message, or it could be WT_ASSERT_ALWAYS.

Note that the pl_get_complete_checkpoint function pointer is currently optional, so we should perform this check only if it is not NULL.