[DO-NOT-MERGE] Rewrite spark.catalog in SQL DDL formatted text

sql/api/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseLexer.g4

@@ -159,6 +159,7 @@ BUCKETS: 'BUCKETS';
 BY: 'BY';
 BYTE: 'BYTE';
 CACHE: 'CACHE';
+CACHED: 'CACHED';
 CALL: 'CALL';
 CALLED: 'CALLED';
 CASCADE: 'CASCADE';

sql/api/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseParser.g4

@@ -375,6 +375,7 @@ statement
     | SHOW PROCEDURES ((FROM | IN) identifierReference)?               #showProcedures
     | SHOW CREATE TABLE identifierReference (AS SERDE)?                #showCreateTable
     | SHOW CURRENT namespace                                           #showCurrentNamespace
+    | SHOW CACHED TABLES                                                #showCachedTables
     | SHOW CATALOGS (LIKE? pattern=stringLit)?                            #showCatalogs
     | (DESC | DESCRIBE) FUNCTION EXTENDED? describeFuncName            #describeFunction
     | (DESC | DESCRIBE) PROCEDURE identifierReference                  #describeProcedure

sql/api/src/main/scala/org/apache/spark/sql/SparkSession.scala

@@ -445,6 +445,38 @@ abstract class SparkSession extends Serializable with Closeable {
    */
   def range(start: Long, end: Long, step: Long, numPartitions: Int): Dataset[lang.Long]
 
+  /**
+   * Parses a multipart identifier (e.g. table or namespace name) into parts.
+   * Used by the Catalog API when building SQL DDL strings.
+   *
+   * @since 4.2.0
+   */
+  def parseMultipartIdentifier(identifier: String): Seq[String]
+
+  /**
+   * Quotes an identifier part for safe use in SQL strings (e.g. backtick-wrapped).
+   * Used by the Catalog API when building SQL DDL strings.
+   *
+   * @since 4.2.0
+   */
+  def quoteIdentifier(identifier: String): String
+
+  /**
+   * Returns the current default database (namespace) in this session.
+   * Used by the Catalog API.
+   *
+   * @since 4.2.0
+   */
+  def currentDatabase: String
+
+  /**
+   * Returns the current default catalog in this session.
+   * Used by the Catalog API.
+   *
+   * @since 4.2.0
+   */
+  def currentCatalog(): String
+
   /* ------------------------- *
    |  Catalog-related methods  |
    * ------------------------- */