Allow to request torrents count via WebAPI

PR #19831.
Closes #19731.

src/webui/api/torrentscontroller.cpp

@@ -234,6 +234,11 @@ namespace
     }
 }
 
+void TorrentsController::countAction()
+{
+    setResult(QString::number(BitTorrent::Session::instance()->torrents().count()));
+}
+
 // Returns all the torrents in JSON format.
 // The return value is a JSON-formatted list of dictionaries.
 // The dictionary keys are: