[SPARK-14284][ML] KMeansSummary deprecating size; adding clusterSizes

## What changes were proposed in this pull request?

KMeansSummary class : deprecated size and added clusterSizes

Author: Shally Sangal <shallysangal@gmail.com>

Closes #12084 from shallys/master.

mllib/src/main/scala/org/apache/spark/ml/clustering/KMeans.scala

@@ -299,7 +299,8 @@ class KMeansSummary private[clustering] (
    * Size of each cluster.
    */
   @Since("2.0.0")
-  lazy val size: Array[Int] = cluster.rdd.map {
+  lazy val clusterSizes: Array[Int] = cluster.rdd.map {
     case Row(clusterIdx: Int) => (clusterIdx, 1)
   }.reduceByKey(_ + _).collect().sortBy(_._1).map(_._2)
+
 }

mllib/src/main/scala/org/apache/spark/ml/r/KMeansWrapper.scala

@@ -37,7 +37,7 @@ private[r] class KMeansWrapper private (
 
   lazy val k: Int = kMeansModel.getK
 
-  lazy val size: Array[Int] = kMeansModel.summary.size
+  lazy val size: Array[Int] = kMeansModel.summary.clusterSizes
 
   lazy val cluster: DataFrame = kMeansModel.summary.cluster