Add proper Diff support for ProjectStateRegistry (#130917)

This change introduces proper diff support for ProjectStateRegistry instead of CompleteDiff and Entry to ProjectStateRegistry, to allow addition of more project state fields in the future

Author: alexey-ivanov-es

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -342,6 +342,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion NODE_USAGE_STATS_FOR_THREAD_POOLS_IN_CLUSTER_INFO = def(9_121_0_00);
     public static final TransportVersion ESQL_CATEGORIZE_OPTIONS = def(9_122_0_00);
     public static final TransportVersion ML_INFERENCE_AZURE_AI_STUDIO_RERANK_ADDED = def(9_123_0_00);
+    public static final TransportVersion PROJECT_STATE_REGISTRY_ENTRY = def(9_124_0_00);
 
     /*
      * STOP! READ THIS FIRST! No, really,

server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java

@@ -835,10 +835,6 @@ private Iterator<? extends ToXContent> toXContentChunkedWithSingleProjectFormat(
         );
     }
 
-    private static final DiffableUtils.KeySerializer<ProjectId> PROJECT_ID_SERIALIZER = DiffableUtils.getWriteableKeySerializer(
-        ProjectId.READER
-    );
-
     private static class MetadataDiff implements Diff<Metadata> {
 
         private final long version;
@@ -880,7 +876,7 @@ private static class MetadataDiff implements Diff<Metadata> {
                 multiProject = null;
             } else {
                 singleProject = null;
-                multiProject = DiffableUtils.diff(before.projectMetadata, after.projectMetadata, PROJECT_ID_SERIALIZER);
+                multiProject = DiffableUtils.diff(before.projectMetadata, after.projectMetadata, ProjectId.PROJECT_ID_SERIALIZER);
             }
 
             if (empty) {
@@ -1004,7 +1000,7 @@ private MetadataDiff(StreamInput in) throws IOException {
                 singleProject = null;
                 multiProject = DiffableUtils.readJdkMapDiff(
                     in,
-                    PROJECT_ID_SERIALIZER,
+                    ProjectId.PROJECT_ID_SERIALIZER,
                     ProjectMetadata::readFrom,
                     ProjectMetadata.ProjectMetadataDiff::new
                 );
@@ -1059,7 +1055,7 @@ public void writeTo(StreamOutput out) throws IOException {
                 if (multiProject != null) {
                     multiProject.writeTo(out);
                 } else {
-                    DiffableUtils.singleEntryDiff(DEFAULT_PROJECT_ID, singleProject, PROJECT_ID_SERIALIZER).writeTo(out);
+                    DiffableUtils.singleEntryDiff(DEFAULT_PROJECT_ID, singleProject, ProjectId.PROJECT_ID_SERIALIZER).writeTo(out);
                 }
             }
         }

server/src/main/java/org/elasticsearch/cluster/metadata/ProjectId.java

@@ -9,6 +9,7 @@
 
 package org.elasticsearch.cluster.metadata;
 
+import org.elasticsearch.cluster.DiffableUtils;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -26,6 +27,7 @@ public class ProjectId implements Writeable, ToXContent {
     private static final String DEFAULT_STRING = "default";
     public static final ProjectId DEFAULT = new ProjectId(DEFAULT_STRING);
     public static final Reader<ProjectId> READER = ProjectId::readFrom;
+    public static final DiffableUtils.KeySerializer<ProjectId> PROJECT_ID_SERIALIZER = DiffableUtils.getWriteableKeySerializer(READER);
     private static final int MAX_LENGTH = 128;
 
     private final String id;