Building .NET Core solutions using Visual Studio for Mac

[guardrex]

Fixes #1743

Notes

• Minor change to windows prepreqs in passing here
• Prereqs section: No single bullet there on one prereq unless you want it. I'm not a big fan of the single bullet list. Let me know.
• Took my liberties with the unit test part. IMO there's no super-fast way to do it. I didn't want to only do a Fact or skip to only a Theory. By the time you do both, it extends the experience to the max for a introductory tutorial. However in defense of this approach, there isn't enough unit testing in the world imo. Devs prob need to see how easy and useful they are.
• On the ASP.NET Core side, we did put links to open GH work issues for missing features. I did that here with the bit on the test runner not working in VS for Mac. I can pull that line if you like. If the line stays, I'm monitoring that issue, and I'll submit a PR to remove it and update the text/images when they get it fixed.
• ... and this one was a real pleasure. 😀 I like Macs, and I don't get enough time to mess around with my Mac Mini. It performed beautifully here! Tip of the 🎩 to Apple! 🍻

[dnfclas]

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[guardrex]

cc/ @bleroy -- If you're reviewing, the drafts are finished.

[BillWagner]

I reviewed everything, and it LGTM.
@bleroy Do you want to review as well, or should we ?

[BillWagner]

I read through everything, and have no issues.

[bleroy]

I did give it a look, and it looks good to me.

[guardrex]

Thanks guys ..... all new content here and my first time using the Mac with .NET Core, so I greatly appreciate the 👀 on it.

[bleroy]

@BillWagner @mairaw I suppose the only question I would have is not about this PR specifically, but about what happened to the VS Mac work I did a few months ago (see https://github.com/dotnet/docs/commits/vs-mac-golden-path) as I can't find this in the current TOC.

[BillWagner]

@bleroy I'm going to defer to @mairaw on that one.

[guardrex]

@bleroy This was a rather extensive rewrite starting with the direction you took. Elements of what you did come thru here, and I thank you for that and the docs on this PR benefit greatly from your work.