XWIKI-9523: Solr indexing queue doesn't decrease anymore after a server restart
* Initialize the index and resolve queues before starting the threads that use them.
XWIKI-9524: Exception thrown when closing XWiki and the Solr indexing queue is full
* Close Sorl threads by sending the signal first to the resolver thread which in turns sends the signal to the indexer thread.
* Use non-blocking and fail-safe API to send the signal (i.e. add the special entry in the BlockingQueue).
XWIKI-9525: Incomplete search results when Solr indexing queue capacity is reached
* Use API that blocks when the queue is full so that the resolver thread waits for the indexer thread to add documents to the Solr index when the queue is full.
* Also don't hard-code IndexOperation.DELETE, pass the actual index operation.