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.
(cherry picked from commit 3ec913d574841f586f826bcf81cbf8ede15720fc)
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).
(cherry picked from commit b0e7cc49b2a57b3aee2642618194410f254d0e51)
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.
(cherry picked from commit 82da406a116e849a08e23c2c5e3a55f2e02710df)