[SPARK-21213][SQL][FOLLOWUP] Use compatible types for comparisons in compareAndGetNewStats

## What changes were proposed in this pull request?
This pr fixed code to compare values in `compareAndGetNewStats`.
The test below fails in the current master;
```
    val oldStats2 = CatalogStatistics(sizeInBytes = BigInt(Long.MaxValue) * 2)
    val newStats5 = CommandUtils.compareAndGetNewStats(
      Some(oldStats2), newTotalSize = BigInt(Long.MaxValue) * 2, None)
    assert(newStats5.isEmpty)
```

## How was this patch tested?
Added some tests in `CommandUtilsSuite`.

Author: Takeshi Yamamuro <yamamuro@apache.org>

Closes #20245 from maropu/SPARK-21213-FOLLOWUP.

sql/core/src/main/scala/org/apache/spark/sql/execution/command/CommandUtils.scala

@@ -116,8 +116,8 @@ object CommandUtils extends Logging {
       oldStats: Option[CatalogStatistics],
       newTotalSize: BigInt,
       newRowCount: Option[BigInt]): Option[CatalogStatistics] = {
-    val oldTotalSize = oldStats.map(_.sizeInBytes.toLong).getOrElse(-1L)
-    val oldRowCount = oldStats.flatMap(_.rowCount.map(_.toLong)).getOrElse(-1L)
+    val oldTotalSize = oldStats.map(_.sizeInBytes).getOrElse(BigInt(-1))
+    val oldRowCount = oldStats.flatMap(_.rowCount).getOrElse(BigInt(-1))
     var newStats: Option[CatalogStatistics] = None
     if (newTotalSize >= 0 && newTotalSize != oldTotalSize) {
       newStats = Some(CatalogStatistics(sizeInBytes = newTotalSize))

sql/core/src/test/scala/org/apache/spark/sql/execution/command/CommandUtilsSuite.scala

@@ -0,0 +1,56 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.command
+
+import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.catalyst.catalog.CatalogStatistics
+
+class CommandUtilsSuite extends SparkFunSuite {
+
+  test("Check if compareAndGetNewStats returns correct results") {
+    val oldStats1 = CatalogStatistics(sizeInBytes = 10, rowCount = Some(100))
+    val newStats1 = CommandUtils.compareAndGetNewStats(
+      Some(oldStats1), newTotalSize = 10, newRowCount = Some(100))
+    assert(newStats1.isEmpty)
+    val newStats2 = CommandUtils.compareAndGetNewStats(
+      Some(oldStats1), newTotalSize = -1, newRowCount = None)
+    assert(newStats2.isEmpty)
+    val newStats3 = CommandUtils.compareAndGetNewStats(
+      Some(oldStats1), newTotalSize = 20, newRowCount = Some(-1))
+    assert(newStats3.isDefined)
+    newStats3.foreach { stat =>
+      assert(stat.sizeInBytes === 20)
+      assert(stat.rowCount.isEmpty)
+    }
+    val newStats4 = CommandUtils.compareAndGetNewStats(
+      Some(oldStats1), newTotalSize = -1, newRowCount = Some(200))
+    assert(newStats4.isDefined)
+    newStats4.foreach { stat =>
+      assert(stat.sizeInBytes === 10)
+      assert(stat.rowCount.isDefined && stat.rowCount.get === 200)
+    }
+  }
+
+  test("Check if compareAndGetNewStats can handle large values") {
+    // Tests for large values
+    val oldStats2 = CatalogStatistics(sizeInBytes = BigInt(Long.MaxValue) * 2)
+    val newStats5 = CommandUtils.compareAndGetNewStats(
+      Some(oldStats2), newTotalSize = BigInt(Long.MaxValue) * 2, None)
+    assert(newStats5.isEmpty)
+  }
+}