Fix debugging, and various other improvements

I have fixed debugging on macOS, which was completely broken, and implemented the "Debug on sample" command. Both debugging with user input and with a sample should now work on all platforms.

Debugging with a sample on macOS always shows a prompt that the program you want to debug requests access to files in "Documents". It works even if you deny the request, so the access is not needed. I have not figured out a way to disable the prompt.

There are also various other convenience improvements, and some maintenance.