Address the comments of 3929 followup

Signed-off-by: Lantao Jin <ltjin@amazon.com>

Author: LantaoJin

core/src/main/java/org/opensearch/sql/calcite/CalcitePlanContext.java

@@ -36,6 +36,7 @@ public class CalcitePlanContext {
   public final QueryType queryType;
   public final Integer querySizeLimit;
 
+  /** This thread local variable is only used to skip script encoding in script pushdown. */
   public static final ThreadLocal<Boolean> skipEncoding = ThreadLocal.withInitial(() -> false);
 
   @Getter @Setter private boolean isResolvingJoinCondition = false;

integ-test/src/test/java/org/opensearch/sql/ppl/PPLIntegTestCase.java

@@ -7,7 +7,6 @@
 
 import static org.opensearch.sql.legacy.TestUtils.getResponseBody;
 import static org.opensearch.sql.plugin.rest.RestPPLQueryAction.EXPLAIN_API_ENDPOINT;
-import static org.opensearch.sql.plugin.rest.RestPPLQueryAction.EXTENDED_EXPLAIN_API_ENDPOINT;
 import static org.opensearch.sql.plugin.rest.RestPPLQueryAction.QUERY_API_ENDPOINT;
 
 import com.google.common.io.Resources;
@@ -32,6 +31,8 @@
 
 /** OpenSearch Rest integration test base for PPL testing. */
 public abstract class PPLIntegTestCase extends SQLIntegTestCase {
+  private static final String EXTENDED_EXPLAIN_API_ENDPOINT =
+      "/_plugins/_ppl/_explain?format=extended";
   private static final Logger LOG = LogManager.getLogger();
 
   @Override

plugin/src/main/java/org/opensearch/sql/plugin/rest/RestPPLQueryAction.java

@@ -41,8 +41,6 @@
 public class RestPPLQueryAction extends BaseRestHandler {
   public static final String QUERY_API_ENDPOINT = "/_plugins/_ppl";
   public static final String EXPLAIN_API_ENDPOINT = "/_plugins/_ppl/_explain";
-  public static final String EXTENDED_EXPLAIN_API_ENDPOINT =
-      "/_plugins/_ppl/_explain?format=extended";
 
   private static final Logger LOG = LogManager.getLogger();