pqPluginDocumentationBehavior: fix indexing documentation
There was never an initial trigger of the refreshHelpEngine slot, so
trigger the timer upon construction. Also change the plugin update loop
to trigger a single time after adding all resources rather than per
resource.
Converting to QTimer::singleShot static calls instead as a QTimer
instance that is single-shot ignores subsequent start() calls.
Fixes: #21772 (closed)
I managed to make 5.12 work by using GammaRay to trigger the reindexDocumentation slot on the internal QHelpSearchEngine object manually.
Cc: @spiros.tsalikis @mwestphal
Backport: release