[SPARK-34952][SQL][FOLLOWUP] Move aggregates to a separate package

### What changes were proposed in this pull request?
Add `aggregate` package under `sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions` and move all the aggregates (e.g. `Count`, `Max`, `Min`, etc.) there.

### Why are the changes needed?
Right now these aggregates are under `sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions`. It looks OK now, but we plan to add a new `filter` package under `expressions` for all the DSV2 filters. It will look strange that filters have their own package, but aggregates don't.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
Existing tests

Closes #33815 from huaxingao/agg_package.

Authored-by: Huaxin Gao <huaxin_gao@apple.com>
Signed-off-by: Liang-Chi Hsieh <viirya@gmail.com>

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/AggregateFunc.java

@@ -15,12 +15,13 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
-
-import org.apache.spark.annotation.Evolving;
 
 import java.io.Serializable;
 
+import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.Expression;
+
 /**
  * Base class of the Aggregate Functions.
  *

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/Aggregation.java

@@ -15,12 +15,13 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
-
-import org.apache.spark.annotation.Evolving;
 
 import java.io.Serializable;
 
+import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.FieldReference;
+
 /**
  * Aggregation in SQL statement.
  *

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/Count.java

@@ -15,9 +15,10 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
 
 import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.FieldReference;
 
 /**
  * An aggregate function that returns the number of the specific row in a group.

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/CountStar.java

@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
 
 import org.apache.spark.annotation.Evolving;
 

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/Max.java

@@ -15,9 +15,10 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
 
 import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.FieldReference;
 
 /**
  * An aggregate function that returns the maximum value in a group.

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/Min.java

@@ -15,9 +15,10 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
 
 import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.FieldReference;
 
 /**
  * An aggregate function that returns the minimum value in a group.

sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/aggregate/Sum.java

@@ -15,9 +15,10 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql.connector.expressions;
+package org.apache.spark.sql.connector.expressions.aggregate;
 
 import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.FieldReference;
 
 /**
  * An aggregate function that returns the summation of all the values in a group.

sql/catalyst/src/main/java/org/apache/spark/sql/connector/read/SupportsPushDownAggregates.java

@@ -18,7 +18,7 @@
 package org.apache.spark.sql.connector.read;
 
 import org.apache.spark.annotation.Evolving;
-import org.apache.spark.sql.connector.expressions.Aggregation;
+import org.apache.spark.sql.connector.expressions.aggregate.Aggregation;
 
 /**
  * A mix-in interface for {@link ScanBuilder}. Data sources can implement this interface to

sql/core/src/main/scala/org/apache/spark/sql/execution/DataSourceScanExec.scala

@@ -31,7 +31,7 @@ import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.QueryPlan
 import org.apache.spark.sql.catalyst.plans.physical.{HashPartitioning, Partitioning, UnknownPartitioning}
 import org.apache.spark.sql.catalyst.util.truncatedString
-import org.apache.spark.sql.connector.expressions.Aggregation
+import org.apache.spark.sql.connector.expressions.aggregate.Aggregation
 import org.apache.spark.sql.execution.datasources._
 import org.apache.spark.sql.execution.datasources.parquet.{ParquetFileFormat => ParquetSource}
 import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceStrategy.scala

@@ -40,7 +40,8 @@ import org.apache.spark.sql.catalyst.rules.Rule
 import org.apache.spark.sql.catalyst.streaming.StreamingRelationV2
 import org.apache.spark.sql.connector.catalog.SupportsRead
 import org.apache.spark.sql.connector.catalog.TableCapability._
-import org.apache.spark.sql.connector.expressions.{AggregateFunc, Count, CountStar, FieldReference, Max, Min, Sum}
+import org.apache.spark.sql.connector.expressions.FieldReference
+import org.apache.spark.sql.connector.expressions.aggregate.{AggregateFunc, Count, CountStar, Max, Min, Sum}
 import org.apache.spark.sql.errors.QueryCompilationErrors
 import org.apache.spark.sql.execution.{InSubqueryExec, RowDataSourceScanExec, SparkPlan}
 import org.apache.spark.sql.execution.command._

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRDD.scala

@@ -25,7 +25,7 @@ import org.apache.spark.{InterruptibleIterator, Partition, SparkContext, TaskCon
 import org.apache.spark.internal.Logging
 import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.catalyst.InternalRow
-import org.apache.spark.sql.connector.expressions.{AggregateFunc, Count, CountStar, Max, Min, Sum}
+import org.apache.spark.sql.connector.expressions.aggregate.{AggregateFunc, Count, CountStar, Max, Min, Sum}
 import org.apache.spark.sql.jdbc.{JdbcDialect, JdbcDialects}
 import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types._

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/PushDownUtils.scala

@@ -22,7 +22,8 @@ import scala.collection.mutable
 import org.apache.spark.sql.catalyst.expressions.{AttributeReference, AttributeSet, Expression, NamedExpression, PredicateHelper, SchemaPruning}
 import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
 import org.apache.spark.sql.catalyst.util.CharVarcharUtils
-import org.apache.spark.sql.connector.expressions.{Aggregation, FieldReference}
+import org.apache.spark.sql.connector.expressions.FieldReference
+import org.apache.spark.sql.connector.expressions.aggregate.Aggregation
 import org.apache.spark.sql.connector.read.{Scan, ScanBuilder, SupportsPushDownAggregates, SupportsPushDownFilters, SupportsPushDownRequiredColumns}
 import org.apache.spark.sql.connector.read.{Scan, ScanBuilder, SupportsPushDownFilters, SupportsPushDownRequiredColumns}
 import org.apache.spark.sql.execution.datasources.DataSourceStrategy

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDown.scala

@@ -25,7 +25,7 @@ import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
 import org.apache.spark.sql.catalyst.planning.ScanOperation
 import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Filter, LeafNode, LogicalPlan, Project}
 import org.apache.spark.sql.catalyst.rules.Rule
-import org.apache.spark.sql.connector.expressions.Aggregation
+import org.apache.spark.sql.connector.expressions.aggregate.Aggregation
 import org.apache.spark.sql.connector.read.{Scan, ScanBuilder, SupportsPushDownAggregates, SupportsPushDownFilters, V1Scan}
 import org.apache.spark.sql.execution.datasources.DataSourceStrategy
 import org.apache.spark.sql.sources

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/jdbc/JDBCScanBuilder.scala

@@ -20,7 +20,7 @@ import scala.util.control.NonFatal
 
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql.SparkSession
-import org.apache.spark.sql.connector.expressions.Aggregation
+import org.apache.spark.sql.connector.expressions.aggregate.Aggregation
 import org.apache.spark.sql.connector.read.{Scan, ScanBuilder, SupportsPushDownAggregates, SupportsPushDownFilters, SupportsPushDownRequiredColumns}
 import org.apache.spark.sql.execution.datasources.PartitioningUtils
 import org.apache.spark.sql.execution.datasources.jdbc.{JDBCOptions, JDBCRDD, JDBCRelation}