KAFKA-8559: Allocate ArrayList with correct size in PartitionStates (#6964)

Reviewers: Ismael Juma <ismael@juma.me.uk>

clients/src/main/java/org/apache/kafka/common/internals/PartitionStates.java

@@ -89,7 +89,7 @@ public class PartitionStates<S> {
      * Returns the partition states in order.
      */
     public List<PartitionState<S>> partitionStates() {
-        List<PartitionState<S>> result = new ArrayList<>();
+        List<PartitionState<S>> result = new ArrayList<>(map.size());
         for (Map.Entry<TopicPartition, S> entry : map.entrySet()) {
             result.add(new PartitionState<>(entry.getKey(), entry.getValue()));
         }