Add supportColumnar in DebugExec

Author: HyukjinKwon

sql/core/src/main/scala/org/apache/spark/sql/execution/debug/package.scala

@@ -265,5 +265,7 @@ package object debug {
     override def doExecuteColumnar(): RDD[ColumnarBatch] = {
       child.executeColumnar()
     }
+
+    override def supportsColumnar: Boolean = child.supportsColumnar
   }
 }