Implements Signaler::disconnectAllSlotsAndWait. Disconnect all slots, if any, connected to this signaler. Any signals emitted on the corresponding signaler that happens after this call to disconnect completes will not call any slots that were connected prior to this call. This function blocks the calling thread pending completion of all ongoing signals being emitted on the signaler. Throws nothing. The behavior is undefined if this method is called from a slot connected to the signaler. Note that it is unspecified how many slots, if any, will be called by any invocation on the signaler that begins before this function completes. Also note that if a slot is connected to this signaler during a call to this function, it is unspecified whether that slot will be disconnected.