Optimize hook to indexed_search that checks for a running crawler task
In indexed_search there's a hook defined that gets called from TSFE->headerNoCache() to determine whether the crawler is currently running. However, to do that simple check, the whole indexer PHP class file is loaded which could be avoided.
Thus, the method user for this hook gets extracted to a slim separate file.
Profiling tests show that this call took 10ms before and 1ms afterwards.
(issue imported from #M11033)