CI: Update/re-examine Visual Studio versions

[squeek502]

Our MSVC versions in CI are getting out-of-date, might want to update them and potentially drop some of the older versions. Right now we test 2017 as the 'main' version and then 2015/2019 for a few targets:

https://ci.appveyor.com/project/racker-buildbot/luv/builds/42820581

EDIT: Libuv tests 2017 / 2019 / 2022 in CI, and their README mentions that MSVC 2015 works (but the README is likely outdated as the most recent version it mentions is 2017, so unsure if they plan to support 2015 as a minimum version).

[squeek502]

I'm thinking about keeping the current 2015 tests, and then moving the rest to just use 2022. That way we can ensure we maintain a minimum supported MSVC (2015) and ensure that we build using the latest version. We won't ensure that the in-between versions will still build properly, but it seems somewhat unlikely that we would introduce problems specific to an in-between version.