[Spark] InCommitTimestamp: Use clock.currentTimeMillis() instead of nanoTime() in commitLarge (#3111)

## Description
We currently use NANOSECONDS.toMillis(System.nanoTime()) for generating
the ICT when `commitLarge` is called. However, this usage of
System.nanoTime() is not correct as it should only be used for measuring
time difference, not to get an approximate wall clock time. This leads
to scenarios where the ICT becomes very small (e.g. 1 Jan 1970)
sometimes because some systems return a very small number when
System.nanoTime() is called. This PR changes this so that
clock.getCurrentTimeMillis() is used instead.

## How was this patch tested?
Added a test case to ensure that `clock.getCurrentTimeMillis()` is being
used.

Author: dhruvarya-db

spark/src/main/scala/org/apache/spark/sql/delta/OptimisticTransaction.scala

@@ -1337,10 +1337,11 @@ trait OptimisticTransactionImpl extends TransactionalWrite
 
     try {
       val tags = Map.empty[String, String]
+      val commitTimestampMs = clock.getTimeMillis()
       val commitInfo = CommitInfo(
-        NANOSECONDS.toMillis(commitStartNano),
+        commitTimestampMs,
         operation = op.name,
-        generateInCommitTimestampForFirstCommitAttempt(NANOSECONDS.toMillis(commitStartNano)),
+        generateInCommitTimestampForFirstCommitAttempt(commitTimestampMs),
         operationParameters = op.jsonEncodedValues,
         context,
         readVersion = Some(readVersion),

spark/src/test/scala/org/apache/spark/sql/delta/InCommitTimestampSuite.scala

@@ -143,6 +143,44 @@ class InCommitTimestampSuite
     }
   }
 
+  for (useCommitLarge <- BOOLEAN_DOMAIN)
+  test("txn.commit should use clock.currentTimeMillis() for ICT" +
+    s" [useCommitLarge: $useCommitLarge]") {
+    withTempDir { tempDir =>
+      spark.range(2).write.format("delta").save(tempDir.getAbsolutePath)
+      // Clear the DeltaLog cache so that a new DeltaLog is created with the manual clock.
+      DeltaLog.clearCache()
+      val expectedCommit1Time = System.currentTimeMillis()
+      val clock = new ManualClock(expectedCommit1Time)
+      val deltaLog = DeltaLog.forTable(spark, new Path(tempDir.getCanonicalPath), clock)
+      val ver0Snapshot = deltaLog.snapshot
+      assert(DeltaConfigs.IN_COMMIT_TIMESTAMPS_ENABLED.fromMetaData(ver0Snapshot.metadata))
+      val usageRecords = Log4jUsageLogger.track {
+        if (useCommitLarge) {
+          deltaLog.startTransaction().commitLarge(
+            spark,
+            Seq(createTestAddFile("1")).toIterator,
+            newProtocolOpt = None,
+            DeltaOperations.ManualUpdate,
+            context = Map.empty,
+            metrics = Map.empty)
+        } else {
+          deltaLog.startTransaction().commit(
+            Seq(createTestAddFile("1")),
+            DeltaOperations.ManualUpdate,
+            tags = Map.empty
+          )
+        }
+      }
+      val ver1Snapshot = deltaLog.snapshot
+      val retrievedTimestamp = getInCommitTimestamp(deltaLog, version = 1)
+      assert(ver1Snapshot.timestamp == retrievedTimestamp)
+      assert(ver1Snapshot.timestamp == expectedCommit1Time)
+      val expectedOpType = if (useCommitLarge) "delta.commit.large" else "delta.commit"
+      assert(filterUsageRecords(usageRecords, expectedOpType).length == 1)
+    }
+  }
+
   test("Missing CommitInfo should result in a DELTA_MISSING_COMMIT_INFO exception") {
     withTempDir { tempDir =>
       spark.range(10).write.format("delta").save(tempDir.getAbsolutePath)