When a shard becomes search active then trigger a refresh instead of waiting for the next scheduled refresh.
The `IndexShard#awaitShardSearchActive(...)` method registers a refresh listener and then often waits for the refresh scheduler to trigger a refresh. By default this is one second. In order to avoid increasing the query time of the Search API, the mentioned method should trigger a refresh instead for waiting it to happen.

As part of this change we also need to disable the refresh scheduler completely. Otherwise we run at risk of running two refreshes next after each other. One triggered from making shard search active and one from the refresh scheduler.  



server/src/main/java/org/elasticsearch/index/shard/IndexShard.java
* Acquires a point-in-time reader that can be used to create {@link Engine.Searcher}s on demand.
     */
    public Engine.SearcherSupplier acquireSearcherSupplier() {
        return acquireSearcherSupplier(Engine.SearcherScope.EXTERNAL);
    }
    /**
     * Acquires a point-in-time reader that can be used to create {@link Engine.Searcher}s on demand.
     */
    public Engine.SearcherSupplier acquireSearcherSupplier(Engine.SearcherScope scope) {
        readAllowed();
        markSearcherAccessed();
        final Engine engine = getEngine();
        return engine.acquireSearcherSupplier(this::wrapSearcher, scope);
    }
    public Engine.Searcher acquireSearcher(String source) {
        readAllowed();
        markSearcherAccessed();
        final Engine engine = getEngine();
        return engine.acquireSearcher(source, Engine.SearcherScope.EXTERNAL, this::wrapSearcher);
    }
    private void markSearcherAccessed() {
        lastSearcherAccess.lazySet(threadPool.relativeTimeInMillis());
    }
    private Engine.Searcher wrapSearcher(Engine.Searcher searcher) {
        assert ElasticsearchDirectoryReader.unwrap(searcher.getDirectoryReader()) != null
            : "DirectoryReader must be an instance or ElasticsearchDirectoryReader";
        boolean success = false;
        try {
            final Engine.Searcher newSearcher = wrapSearcher(searcher, fieldUsageTracker.createSession(), readerWrapper);
            assert newSearcher != null;