Avoid building O(N) list in can_match phase (elastic#112458)

We can be a little faster and memory efficient here by not building a
list of shard requests up-front and instead building them as we need
them.

Author: original-brownbear

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

@@ -229,10 +229,6 @@ public List<Shard> getShardLevelRequests() {
         return shards;
     }
 
-    public List<ShardSearchRequest> createShardSearchRequests() {
-        return shards.stream().map(this::createShardSearchRequest).toList();
-    }
-
     public ShardSearchRequest createShardSearchRequest(Shard r) {
         ShardSearchRequest shardSearchRequest = new ShardSearchRequest(
             new OriginalIndices(r.indices, indicesOptions),

server/src/main/java/org/elasticsearch/search/SearchService.java

@@ -1664,13 +1664,11 @@ public AliasFilter buildAliasFilter(ClusterState state, String index, Set<String
     }
 
     public void canMatch(CanMatchNodeRequest request, ActionListener<CanMatchNodeResponse> listener) {
-        final List<ShardSearchRequest> shardSearchRequests = request.createShardSearchRequests();
-        final List<CanMatchNodeResponse.ResponseOrFailure> responses = new ArrayList<>(shardSearchRequests.size());
-        for (ShardSearchRequest shardSearchRequest : shardSearchRequests) {
-            CanMatchShardResponse canMatchShardResponse;
+        var shardLevelRequests = request.getShardLevelRequests();
+        final List<CanMatchNodeResponse.ResponseOrFailure> responses = new ArrayList<>(shardLevelRequests.size());
+        for (var shardLevelRequest : shardLevelRequests) {
             try {
-                canMatchShardResponse = canMatch(shardSearchRequest);
-                responses.add(new CanMatchNodeResponse.ResponseOrFailure(canMatchShardResponse));
+                responses.add(new CanMatchNodeResponse.ResponseOrFailure(canMatch(request.createShardSearchRequest(shardLevelRequest))));
             } catch (Exception e) {
                 responses.add(new CanMatchNodeResponse.ResponseOrFailure(e));
             }