Use BoostQuery rather than FunctionScoreQuery for query-time indices_boost (#52272)

This is a trivial change, but it should result in a slightly more efficient query boost.

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

@@ -21,6 +21,7 @@ package org.elasticsearch.search;
 
 import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
+import org.apache.lucene.search.BoostQuery;
 import org.apache.lucene.search.Collector;
 import org.apache.lucene.search.FieldDoc;
 import org.apache.lucene.search.MatchNoDocsQuery;
@@ -31,8 +32,6 @@ import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.lease.Releasables;
 import org.elasticsearch.common.lucene.search.Queries;
-import org.elasticsearch.common.lucene.search.function.FunctionScoreQuery;
-import org.elasticsearch.common.lucene.search.function.WeightFactorFunction;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.BigArrays;
 import org.elasticsearch.index.IndexService;
@@ -248,7 +247,7 @@ final class DefaultSearchContext extends SearchContext {
             parsedQuery(ParsedQuery.parsedMatchAllQuery());
         }
         if (queryBoost() != AbstractQueryBuilder.DEFAULT_BOOST) {
-            parsedQuery(new ParsedQuery(new FunctionScoreQuery(query(), new WeightFactorFunction(queryBoost)), parsedQuery()));
+            parsedQuery(new ParsedQuery(new BoostQuery(query(), queryBoost), parsedQuery()));
         }
         this.query = buildFilteredQuery(query);
         if (rewrite) {