Add systempath grain

[terminalmage]

This provides a grain like pythonpath, only for the system path. In
other words, it's the value of the PATH environment variable, only
formatted as a list of directories.

Resolves #49049.

[terminalmage]

I rebased to resolve merge conflicts.

[terminalmage]

@DmitryKuzmenko When I rebased, it looks like I lost your review. I can't find the old review comments, either. Did you have any concerns?

One thing to note is that I used the wrong name in the Pull Request title, it should have been systempath instead of systemtest. I have renamed the PR to reflect this.

[DmitryKuzmenko]

@terminalmage if I remember correctly I've just approved this. =)

[terminalmage]

OK, the GitHub web interface was showing that your earlier review was a "comment" review instead of an approval, so I wanted to be sure.

... and there is now another merge conflict, so I will have to rebase again.

[terminalmage]

Oh great... guess most of my PRs are going to need a rebase now that this harebrained quest to use black has been pushed through.

Good to see that the important things are getting done... 🙄

[DmitryKuzmenko]

Yep, unfortunately.

[terminalmage]

Looks like you'll need to re-review, again.