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

db_stress_tool/no_batched_ops_stress.cc

@@ -60,11 +60,8 @@ class NonBatchedOpsStressTest : public StressTest {
       constexpr int num_methods =
           static_cast<int>(VerificationMethod::kNumberOfMethods);
 
-      // Note: Merge/GetMergeOperands is currently not supported for wide-column
-      // entities
       const VerificationMethod method =
-          static_cast<VerificationMethod>(thread->rand.Uniform(
-              FLAGS_use_put_entity_one_in > 0 ? num_methods - 1 : num_methods));
+          static_cast<VerificationMethod>(thread->rand.Uniform(num_methods));
 
       if (method == VerificationMethod::kIterator) {
         std::unique_ptr<Iterator> iter(