Scripting: Add an "Exit2:" command that will exit without prompting to save the project

[SteveDaulton]

Is your feature request related to a problem? Please describe.
When driving Audacity via mod-script-pipe, the user may want to shut down the computer on completion. This cannot be done conveniently because after sending the "Exit:" command, Audacity prompts to save the project (even if it is empty).

Describe the solution you'd like
A new command "Exit2:" that is available for scripting that will quit Audacity without prompting to save.

Describe alternatives you've considered
Issue the commands:

1. Select All
2. Remove Tracks (project is now empty)
3. Select 1 second (any small amount will do - we don't want to be using a lot of disk space)
4. Generate silence (or generate anything else - this is just to avoid being prompted about saving an empty project)
5. SaveProject2: (save it somewhere convenient)
6. Exit:
7. and then delete the unwanted AUP3 using the scripting language.

While this solution works, it is not convenient, and it is platform dependent (for saving and deleting the unwanted AUP3 file)

Additional context
Suggested on the forum here: https://forum.audacityteam.org/viewtopic.php?p=440395#p440395