Add name to threads

This help identifying threads when debugging.
The naming scheme is using 'class/function name + variable name'.
Note that the length limitaion is 16 chars on linux. On Windows, the limit is 32767 chars.

PR #21403.

src/base/bittorrent/sessionimpl.h

@@ -57,7 +57,6 @@
 #include "trackerentrystatus.h"
 
 class QString;
-class QThread;
 class QThreadPool;
 class QTimer;
 class QUrl;