Support using GetMergeOperands for verification with wide columns (#10952)

Support using GetMergeOperands for verification with wide columns (#10952)

Summary:
With the recent changes, `GetMergeOperands` is now supported for wide-column entities as well, so we can use it for verification purposes in the non-batched stress tests.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10952

Test Plan: Ran a simple non-batched ops blackbox crash test.

Reviewed By: riversand963

Differential Revision: D41292114

Pulled By: ltamasi

fbshipit-source-id: 70b4c756a4a1fecb445c16c7096aad805a51203c