Address minor review comments

Author: alexey-ivanov-es

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

@@ -2059,7 +2059,7 @@ static boolean assertDataStreams(Map<String, IndexMetadata> indices, DataStreamM
             return true;
         }
 
-        @FixForMultiProject(description = "Remove reading reserved_state and settings")
+        @FixForMultiProject(description = "Remove reading reserved_state and settings") // ES-12795
         public static ProjectMetadata fromXContent(XContentParser parser) throws IOException {
             XContentParser.Token token = parser.currentToken();
             if (token == null) {
@@ -2080,7 +2080,7 @@ public static ProjectMetadata fromXContent(XContentParser parser) throws IOExcep
                     }
                 } else if (token == XContentParser.Token.START_OBJECT) {
                     switch (currentFieldName) {
-                        // Remove this
+                        // Remove this (ES-12795)
                         case "reserved_state" -> {
                             while (parser.nextToken() != XContentParser.Token.END_OBJECT) {
                                 ReservedStateMetadata.fromXContent(parser);
@@ -2096,7 +2096,7 @@ public static ProjectMetadata fromXContent(XContentParser parser) throws IOExcep
                                 projectBuilder.put(IndexTemplateMetadata.Builder.fromXContent(parser, parser.currentName()));
                             }
                         }
-                        // Remove this
+                        // Remove this (ES-12795)
                         case "settings" -> {
                             Settings.fromXContent(parser);
                         }

server/src/main/java/org/elasticsearch/cluster/project/ProjectStateRegistry.java

@@ -40,7 +40,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.function.Function;
+import java.util.function.UnaryOperator;
 import java.util.stream.Collectors;
 
 /**
@@ -316,7 +316,7 @@ private Builder(ProjectStateRegistry original) {
             this.projectsMarkedForDeletionGeneration = original.projectsMarkedForDeletionGeneration;
         }
 
-        private void updateEntry(ProjectId projectId, Function<Entry, Entry> modifier) {
+        private void updateEntry(ProjectId projectId, UnaryOperator<Entry> modifier) {
             Entry entry = projectsEntries.get(projectId);
             if (entry == null) {
                 entry = new Entry();

server/src/main/java/org/elasticsearch/reservedstate/service/FileSettingsService.java

@@ -32,6 +32,7 @@
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.core.FixForMultiProject;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.health.HealthIndicatorDetails;
 import org.elasticsearch.health.HealthIndicatorImpact;
@@ -131,6 +132,7 @@ public Path watchedFile() {
      * @param mdBuilder    the current metadata builder for the new cluster state
      * @param projectId    the project associated with the restore
      */
+    @FixForMultiProject(description = "Simplify parameters (ES-12796)")
     public void handleSnapshotRestore(
         ClusterState clusterState,
         ClusterState.Builder builder,