[HOT-FIX] Add EvaluatedType back to RDG

87941ff8c4 accidentally removed the EvaluatedType.

Author: Yin Huai <yhuai@databricks.com>

Closes #6589 from yhuai/getBackEvaluatedType and squashes the following commits:

618c2eb [Yin Huai] Add EvaluatedType back.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/random.scala

@@ -38,6 +38,8 @@ abstract class RDG(seed: Long) extends LeafExpression with Serializable {
    */
   @transient protected lazy val rng = new XORShiftRandom(seed + TaskContext.get().partitionId())
 
+  override type EvaluatedType = Double
+
   override def deterministic: Boolean = false
 
   override def nullable: Boolean = false