Toolset update: VS 2019 16.10 Preview 2

[StephanTLavavej]

• Update the toolset to VS 2019 16.10 Preview 2.
  • This also enables VMSS diagnostic logs, now required by policy. The checklist has been updated accordingly.
  • This contains CMake 3.20, now required, which fixes Build system: Codegen messages are noisy #836.
• Change the Update Status Chart workflow to run for microsoft/STL only, as requested by @AdamBucior in Use GitHub Actions to update the Status Chart #1769. I've tested this in my fork.
  • This also increases the required node-version. It doesn't really matter (the workflow always retrieves the latest) but it's a new major version.
• In the Standard Library Header Units test, use /exportHeader /headerName:angle and /headerUnit:angle (supported in Preview 2) to avoid the need for absolute paths.
• Test vector's constexpr spaceships (supported in Preview 2), which fixes <vector>: Test constexpr spaceships #1677.

[miscco]

I hate build systems, but the rest looks great

[fsb4000]

In the Standard Library Header Units test, use /exportHeader /headerName:angle and /headerUnit:angle (supported in Preview 2) to avoid the need for absolute paths.

Great. I didn't know that. It works without absolute paths. Cool!

cl /EHsc /nologo /W4 /std:c++latest /MD  /exportHeader /headerName:angle iostream /Fo:iostream.obj
cl /EHsc /nologo /W4 /std:c++latest /MD  /exportHeader /headerName:angle vector /Fo:vector.obj
cl /EHsc /nologo /W4 /std:c++latest /MD /headerUnit:angle "iostream=iostream.ifc" /headerUnit:angle "vector=vector.ifc" main.cpp iostream.obj vector.obj