[SPARK-42468][CONNECT][FOLLOW-UP] Add .agg variants in Dataset

connector/connect/client/jvm/src/main/scala/org/apache/spark/sql/Dataset.scala

@@ -1058,6 +1058,61 @@ class Dataset[T] private[sql] (val session: SparkSession, private[sql] val plan:
     new RelationalGroupedDataset(toDF(), cols.map(_.expr))
   }
 
+  /**
+   * (Scala-specific) Aggregates on the entire Dataset without groups.
+   * {{{
+   *   // ds.agg(...) is a shorthand for ds.groupBy().agg(...)
+   *   ds.agg("age" -> "max", "salary" -> "avg")
+   *   ds.groupBy().agg("age" -> "max", "salary" -> "avg")
+   * }}}
+   *
+   * @group untypedrel
+   * @since 3.4.0
+   */
+  def agg(aggExpr: (String, String), aggExprs: (String, String)*): DataFrame = {
+    groupBy().agg(aggExpr, aggExprs: _*)
+  }
+
+  /**
+   * (Scala-specific) Aggregates on the entire Dataset without groups.
+   * {{{
+   *   // ds.agg(...) is a shorthand for ds.groupBy().agg(...)
+   *   ds.agg(Map("age" -> "max", "salary" -> "avg"))
+   *   ds.groupBy().agg(Map("age" -> "max", "salary" -> "avg"))
+   * }}}
+   *
+   * @group untypedrel
+   * @since 3.4.0
+   */
+  def agg(exprs: Map[String, String]): DataFrame = groupBy().agg(exprs)
+
+  /**
+   * (Java-specific) Aggregates on the entire Dataset without groups.
+   * {{{
+   *   // ds.agg(...) is a shorthand for ds.groupBy().agg(...)
+   *   ds.agg(Map("age" -> "max", "salary" -> "avg"))
+   *   ds.groupBy().agg(Map("age" -> "max", "salary" -> "avg"))
+   * }}}
+   *
+   * @group untypedrel
+   * @since 3.4.0
+   */
+  def agg(exprs: java.util.Map[String, String]): DataFrame = groupBy().agg(exprs)
+
+  /**
+   * Aggregates on the entire Dataset without groups.
+   * {{{
+   *   // ds.agg(...) is a shorthand for ds.groupBy().agg(...)
+   *   ds.agg(max($"age"), avg($"salary"))
+   *   ds.groupBy().agg(max($"age"), avg($"salary"))
+   * }}}
+   *
+   * @group untypedrel
+   * @since 3.4.0
+   */
+  @scala.annotation.varargs
+  def agg(expr: Column, exprs: Column*): DataFrame = groupBy().agg(expr, exprs: _*)
+
   /**
    * Unpivot a DataFrame from wide format to long format, optionally leaving identifier columns
    * set. This is the reverse to `groupBy(...).pivot(...).agg(...)`, except for the aggregation,