Add shell.package_path setting for package.path defaults

[MCJack123]

This PR simply adds a new setting called shell.package_path, which stores the default package.path value. This allows users and programs to easily add global library paths without having to override cc.require. For instance, this can be used by package managers to add a central directory for shared libraries, instead of requiring programs to have their own copies of common software. The default settings will remain the same, and package.path changes in programs won't affect anything else globally.

[Wojbie]

Related discussion where this was already denied #739

[MCJack123]

I'm thinking of this more from a user-oriented perspective, where the user gets to determine what their own path is (and hopefully a program/package manager would respect the user's wishes), rather than as something for programs to abuse for their own paths. Of course, you can't force programs to not do bad things, but the way things are right now makes it very difficult to have common libraries for your own programs, and I think this is the simplest and most minimally invasive way to fix it.

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OTOH, maybe the reason CI failed is exactly why this is a bad idea. 🙃

If a global setting is a bad idea, then the next best way to resolve this issue is to add inheritance. This keeps the idea of using wrapper programs, but makes it a bit more flexible by allowing the original program to be run with shell.run as usual. It would resolve an annoying sticking point I had while developing Herobrine, where I needed to shell.run each program to get a new environment, but because package.path wasn't inherited, I had to add a line to append the library directory to every single program - this caught me when trying to run it uncompressed from a disk drive, as I had to change the path in every file.

[Lupus590]

If a global setting is a bad idea, then the next best way to resolve this issue is to add inheritance. This keeps the idea of using wrapper programs, but makes it a bit more flexible by allowing the original program to be run with shell.run as usual. It would resolve an annoying sticking point I had while developing Herobrine, where I needed to shell.run each program to get a new environment, but because package.path wasn't inherited, I had to add a line to append the library directory to every single program - this caught me when trying to run it uncompressed from a disk drive, as I had to change the path in every file.

Would os.run be better here?