Avoid I/O operations when rewriting shard search request (#54044) (#54139)

This commit ensures that we rewrite the shard request with a short-lived can_match searcher.
This is required for frozen indices since the high level rewrite is now performed on a network thread where we don't want to perform I/O.

Closes #53985

Author: jimczi

server/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -1228,12 +1228,12 @@ public void failShard(String reason, @Nullable Exception e) {
     }
 
     /**
-     * Acquire the searcher without applying the additional reader wrapper.
+     * Acquire a lightweight searcher which can be used to rewrite shard search requests.
      */
-    public Engine.Searcher acquireSearcherNoWrap(String source) {
+    public Engine.Searcher acquireCanMatchSearcher() {
         readAllowed();
         markSearcherAccessed();
-        return getEngine().acquireSearcher(source, Engine.SearcherScope.EXTERNAL);
+        return getEngine().acquireSearcher("can_match", Engine.SearcherScope.EXTERNAL);
     }
 
     public Engine.Searcher acquireSearcher(String source) {
@@ -1252,10 +1252,7 @@ private Engine.Searcher acquireSearcher(String source, Engine.SearcherScope scop
         return wrapSearcher(searcher);
     }
 
-    /**
-     * Wraps the provided searcher acquired with {@link #acquireSearcherNoWrap(String)}.
-     */
-    public Engine.Searcher wrapSearcher(Engine.Searcher searcher) {
+    private Engine.Searcher wrapSearcher(Engine.Searcher searcher) {
         assert ElasticsearchDirectoryReader.unwrap(searcher.getDirectoryReader())
             != null : "DirectoryReader must be an instance or ElasticsearchDirectoryReader";
         boolean success = false;