This option was invented when single instance check wasn't adapted for -workdir. Now, -workdir can work without -many and this option is redudant, but auto-update prevention is helpful. Let's autodetect whether the binary is already running with a lock file.
This was causing an assertion violation in Ui::PostponeCall.
- Add a generic Core::QtSignalProducer to convert Qt signals to rpl::producer.
- Track event loop nesting inside QtSignalProducer.
- Use QtSignalProducer for QWindow::activeChanged tracking.