Hide ImmutableOpenMap in IndexMetadata (#86589)

IndexMetadata has several ImmutableOpenMaps in its implementation.
However, the getters for those members expose ImmutableOpenMap when Map
works just fine. This commit changes the return types of these methods
from IndexMetadata, so that the IndexMetadata implementation can be
changed independently.

relates #86239

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

@@ -804,7 +804,7 @@ public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragmen
         return settings;
     }
 
-    public ImmutableOpenMap<String, AliasMetadata> getAliases() {
+    public Map<String, AliasMetadata> getAliases() {
         return this.aliases;
     }
 
@@ -881,7 +881,7 @@ public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragmen
     // LifecycleSettings.LIFECYCLE_NAME_SETTING for the 'real' version
     public static final String LIFECYCLE_NAME = "index.lifecycle.name";
 
-    ImmutableOpenMap<String, DiffableStringMap> getCustomData() {
+    Map<String, DiffableStringMap> getCustomData() {
         return this.customData;
     }
 
@@ -893,7 +893,7 @@ public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragmen
         return inSyncAllocationIds;
     }
 
-    public ImmutableOpenMap<String, RolloverInfo> getRolloverInfos() {
+    public Map<String, RolloverInfo> getRolloverInfos() {
         return rolloverInfos;
     }
 

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

@@ -17,7 +17,6 @@ import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexAbstraction.Type;
 import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.logging.DeprecationCategory;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.regex.Regex;
@@ -735,7 +734,7 @@ public class IndexNameExpressionResolver {
                 .map(DataStreamAlias::getName)
                 .toArray(String[]::new);
         } else {
-            final ImmutableOpenMap<String, AliasMetadata> indexAliases = indexMetadata.getAliases();
+            final Map<String, AliasMetadata> indexAliases = indexMetadata.getAliases();
             final AliasMetadata[] aliasCandidates;
             if (iterateIndexAliases(indexAliases.size(), resolvedExpressions.size())) {
                 // faster to iterate indexAliases

server/src/main/java/org/elasticsearch/search/internal/ShardSearchRequest.java

@@ -21,7 +21,6 @@ import org.elasticsearch.common.CheckedBiConsumer;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
-import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.hash.MessageDigests;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -588,7 +587,7 @@ public class ShardSearchRequest extends TransportRequest implements IndicesReque
             return null;
         }
         Index index = metadata.getIndex();
-        ImmutableOpenMap<String, AliasMetadata> aliases = metadata.getAliases();
+        Map<String, AliasMetadata> aliases = metadata.getAliases();
         Function<AliasMetadata, QueryBuilder> parserFunction = (alias) -> {
             if (alias.filter() == null) {
                 return null;