Avoid serialising state if it was already serialised (elastic#39179)

When preparing the state to send to other nodes, we're serializing it for each node, despite using putIfAbsent.
This commit checks if the state was already serialized for this node version before performing the potentially expensive computation.
The map is not used by multiple threads, so computeIfAbsent is not needed (and could not be used here easily, because IOException could be thrown).

Author: andrershov

server/src/main/java/org/elasticsearch/cluster/coordination/PublicationTransportHandler.java

@@ -273,13 +273,17 @@ private static void buildDiffAndSerializeStates(ClusterState clusterState, Clust
             }
             try {
                 if (sendFullVersion || !previousState.nodes().nodeExists(node)) {
-                    serializedStates.putIfAbsent(node.getVersion(), serializeFullClusterState(clusterState, node.getVersion()));
+                    if (serializedStates.containsKey(node.getVersion()) == false) {
+                        serializedStates.put(node.getVersion(), serializeFullClusterState(clusterState, node.getVersion()));
+                    }
                 } else {
                     // will send a diff
                     if (diff == null) {
                         diff = clusterState.diff(previousState);
                     }
-                    serializedDiffs.putIfAbsent(node.getVersion(), serializeDiffClusterState(diff, node.getVersion()));
+                    if (serializedDiffs.containsKey(node.getVersion()) == false) {
+                        serializedDiffs.put(node.getVersion(), serializeDiffClusterState(diff, node.getVersion()));
+                    }
                 }
             } catch (IOException e) {
                 throw new ElasticsearchException("failed to serialize cluster state for publishing to node {}", e, node);