TEST: Disable merges in testRebuildLocalCheckpointTracker (#36625)

In this test, we keep track of a list of index commits then verify that
we reload exactly every operation from the safe commit. If a background
merge is triggered, then we might have a new index commit which is not
recorded in the tracking list. This change disables merges in the test.

Closes #36470

server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -5426,41 +5426,17 @@ public class InternalEngineTests extends EngineTestCase {
         final IndexSettings indexSettings = IndexSettingsModule.newIndexSettings(indexMetaData);
         final AtomicLong globalCheckpoint = new AtomicLong(SequenceNumbers.NO_OPS_PERFORMED);
         Path translogPath = createTempDir();
-        int numOps = scaledRandomIntBetween(1, 500);
-        List<Engine.Operation> operations = new ArrayList<>();
-        for (int i = 0; i < numOps; i++) {
-            long seqNo = i;
-            final ParsedDocument doc = EngineTestCase.createParsedDoc(Integer.toString(between(1, 100)), null);
-            if (randomBoolean()) {
-                operations.add(new Engine.Index(EngineTestCase.newUid(doc), doc, seqNo, primaryTerm.get(),
-                    i, null, Engine.Operation.Origin.REPLICA, threadPool.relativeTimeInMillis(), -1, true, UNASSIGNED_SEQ_NO, 0L));
-            } else if (randomBoolean()) {
-                operations.add(new Engine.Delete(doc.type(), doc.id(), EngineTestCase.newUid(doc), seqNo, primaryTerm.get(),
-                    i, null, Engine.Operation.Origin.REPLICA, threadPool.relativeTimeInMillis(),
-                    UNASSIGNED_SEQ_NO, 0L));
-            } else {
-                operations.add(new Engine.NoOp(seqNo, primaryTerm.get(), Engine.Operation.Origin.REPLICA,
-                    threadPool.relativeTimeInMillis(), "test-" + i));
-            }
-        }
-        Randomness.shuffle(operations);
+        List<Engine.Operation> operations = generateHistoryOnReplica(between(1, 500), randomBoolean(), randomBoolean(), randomBoolean());
         List<List<Engine.Operation>> commits = new ArrayList<>();
         commits.add(new ArrayList<>());
         try (Store store = createStore()) {
-            EngineConfig config = config(indexSettings, store, translogPath,
-                newMergePolicy(), null, null, globalCheckpoint::get);
+            EngineConfig config = config(indexSettings, store, translogPath, NoMergePolicy.INSTANCE, null, null, globalCheckpoint::get);
             final List<DocIdSeqNoAndTerm> docs;
             try (InternalEngine engine = createEngine(config)) {
                 List<Engine.Operation> flushedOperations = new ArrayList<>();
                 for (Engine.Operation op : operations) {
                     flushedOperations.add(op);
-                    if (op instanceof Engine.Index) {
-                        engine.index((Engine.Index) op);
-                    } else if (op instanceof Engine.Delete) {
-                        engine.delete((Engine.Delete) op);
-                    } else {
-                        engine.noOp((Engine.NoOp) op);
-                    }
+                    applyOperation(engine, op);
                     if (randomInt(100) < 10) {
                         engine.refresh("test");
                     }