[SPARK-27480][SQL] Improve EXPLAIN DESC QUERY to show the input SQL statement

Currently running explain on describe query gives a little confusing output. This is a minor pr that improves the output of explain.

Before
```
1.EXPLAIN DESCRIBE WITH s AS (SELECT 'hello' as col1) SELECT * FROM s;
== Physical Plan ==
Execute DescribeQueryCommand
   +- DescribeQueryCommand CTE [s]
2.EXPLAIN EXTENDED DESCRIBE SELECT * from s1 where c1 > 0;
== Physical Plan ==
Execute DescribeQueryCommand
   +- DescribeQueryCommand 'Project [*]
```
After
```
1. EXPLAIN DESCRIBE WITH s AS (SELECT 'hello' as col1) SELECT * FROM s;
== Physical Plan ==
Execute DescribeQueryCommand
   +- DescribeQueryCommand WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
2. EXPLAIN DESCRIBE SELECT * from s1 where c1 > 0;
== Physical Plan ==
Execute DescribeQueryCommand
   +- DescribeQueryCommand SELECT * from s1 where c1 > 0
```
Added a couple of tests in describe-query.sql under SQLQueryTestSuite.

Closes #24385 from dilipbiswal/describe_query_explain.

Authored-by: Dilip Biswal <dbiswal@us.ibm.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

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

@@ -373,7 +373,7 @@ class SparkSqlAstBuilder(conf: SQLConf) extends AstBuilder(conf) {
    * Create a [[DescribeQueryCommand]] logical command.
    */
   override def visitDescribeQuery(ctx: DescribeQueryContext): LogicalPlan = withOrigin(ctx) {
-    DescribeQueryCommand(visitQuery(ctx.query))
+    DescribeQueryCommand(source(ctx.query), visitQuery(ctx.query))
   }
 
   /**

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

@@ -639,12 +639,14 @@ case class DescribeTableCommand(
  *    select * from (from a select * select *)
  * 7. Common table expressions (CTEs)
  */
-case class DescribeQueryCommand(query: LogicalPlan)
+case class DescribeQueryCommand(queryText: String, plan: LogicalPlan)
   extends DescribeCommandBase {
 
+  override def simpleString(maxFields: Int): String = s"$nodeName $queryText".trim
+
   override def run(sparkSession: SparkSession): Seq[Row] = {
     val result = new ArrayBuffer[Row]
-    val queryExecution = sparkSession.sessionState.executePlan(query)
+    val queryExecution = sparkSession.sessionState.executePlan(plan)
     describeSchema(queryExecution.analyzed.schema, result, header = false)
     result
   }

sql/core/src/test/resources/sql-tests/inputs/describe-query.sql

@@ -22,6 +22,10 @@ DESCRIBE
      insert into desc_temp1 select *
      insert into desc_temp2 select *;
 
+-- Explain
+EXPLAIN DESC QUERY SELECT * FROM desc_temp2 WHERE key > 0;
+EXPLAIN EXTENDED DESC WITH s AS (SELECT 'hello' as col1) SELECT * FROM s;
+
 -- cleanup
 DROP TABLE desc_temp1;
 DROP TABLE desc_temp2;

sql/core/src/test/resources/sql-tests/results/describe-query.sql.out

@@ -1,5 +1,5 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 17
+-- Number of queries: 19
 
 
 -- !query 0
@@ -154,16 +154,46 @@ DESCRIBE
 
 
 -- !query 15
-DROP TABLE desc_temp1
+EXPLAIN DESC QUERY SELECT * FROM desc_temp2 WHERE key > 0
 -- !query 15 schema
-struct<>
+struct<plan:string>
 -- !query 15 output
-
+== Physical Plan ==
+Execute DescribeQueryCommand
+   +- DescribeQueryCommand SELECT * FROM desc_temp2 WHERE key > 0
 
 
 -- !query 16
-DROP TABLE desc_temp2
+EXPLAIN EXTENDED DESC WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
 -- !query 16 schema
-struct<>
+struct<plan:string>
 -- !query 16 output
+== Parsed Logical Plan ==
+DescribeQueryCommand WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
+
+== Analyzed Logical Plan ==
+col_name: string, data_type: string, comment: string
+DescribeQueryCommand WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
+
+== Optimized Logical Plan ==
+DescribeQueryCommand WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
+
+== Physical Plan ==
+Execute DescribeQueryCommand
+   +- DescribeQueryCommand WITH s AS (SELECT 'hello' as col1) SELECT * FROM s
+
+
+-- !query 17
+DROP TABLE desc_temp1
+-- !query 17 schema
+struct<>
+-- !query 17 output
+
+
+
+-- !query 18
+DROP TABLE desc_temp2
+-- !query 18 schema
+struct<>
+-- !query 18 output
 

sql/core/src/test/scala/org/apache/spark/sql/execution/SparkSqlParserSuite.scala

@@ -228,8 +228,8 @@ class SparkSqlParserSuite extends AnalysisTest {
 
   test("describe query") {
     val query = "SELECT * FROM t"
-    assertEqual("DESCRIBE QUERY " + query, DescribeQueryCommand(parser.parsePlan(query)))
-    assertEqual("DESCRIBE " + query, DescribeQueryCommand(parser.parsePlan(query)))
+    assertEqual("DESCRIBE QUERY " + query, DescribeQueryCommand(query, parser.parsePlan(query)))
+    assertEqual("DESCRIBE " + query, DescribeQueryCommand(query, parser.parsePlan(query)))
   }
 
   test("describe table column") {