[SPARK-36814][SQL] Make class ColumnarBatch extendable

### What changes were proposed in this pull request?
Change class ColumnarBatch to a non-final class

### Why are the changes needed?
To support better vectorized reading in multiple data source, ColumnarBatch need to be extendable. For example, To support row-level delete(  apache/iceberg#3141) in Iceberg's vectorized read, we need to filter out deleted rows in a batch, which requires ColumnarBatch to be extendable.

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

### How was this patch tested?
No test needed.

Closes #34054 from flyrain/columnarbatch-extendable.

Authored-by: Yufei Gu <yufei_gu@apple.com>
Signed-off-by: DB Tsai <d_tsai@apple.com>

sql/catalyst/src/main/java/org/apache/spark/sql/vectorized/ColumnarBatch.java

@@ -31,7 +31,7 @@
  * the entire data loading process.
  */
 @Evolving
-public final class ColumnarBatch implements AutoCloseable {
+public class ColumnarBatch implements AutoCloseable {
   private int numRows;
   private final ColumnVector[] columns;