Remove redundant list copy in CanMatchNodeRequest (#121700)

We're not mutating that list ever, so lets just use an immutable list
all the way here and avoid at least one round of needless copy.

Author: original-brownbear

server/src/main/java/org/elasticsearch/action/search/CanMatchNodeRequest.java

@@ -136,7 +136,7 @@ public CanMatchNodeRequest(
     ) {
         this.source = getCanMatchSource(searchRequest);
         this.indicesOptions = indicesOptions;
-        this.shards = new ArrayList<>(shards);
+        this.shards = shards;
         this.searchType = searchRequest.searchType();
         this.requestCache = searchRequest.requestCache();
         // If allowPartialSearchResults is unset (ie null), the cluster-level default should have been substituted

server/src/main/java/org/elasticsearch/action/search/CanMatchPreFilterSearchPhase.java

@@ -40,7 +40,6 @@
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicReferenceArray;
 import java.util.function.BiFunction;
-import java.util.stream.Collectors;
 
 import static org.elasticsearch.core.Strings.format;
 import static org.elasticsearch.core.Types.forciblyCast;
@@ -348,10 +347,7 @@ private record SendingTarget(@Nullable String clusterAlias, @Nullable String nod
 
     private CanMatchNodeRequest createCanMatchRequest(Map.Entry<SendingTarget, List<SearchShardIterator>> entry) {
         final SearchShardIterator first = entry.getValue().get(0);
-        final List<CanMatchNodeRequest.Shard> shardLevelRequests = entry.getValue()
-            .stream()
-            .map(this::buildShardLevelRequest)
-            .collect(Collectors.toCollection(ArrayList::new));
+        final List<CanMatchNodeRequest.Shard> shardLevelRequests = entry.getValue().stream().map(this::buildShardLevelRequest).toList();
         assert entry.getValue().stream().allMatch(Objects::nonNull);
         assert entry.getValue()
             .stream()