Fix all MSVC warnings

[embg]

• Fix MSVC with AVX2 compile option, C4244 warnings. #3489
• Add a test to reproduce MSVC with AVX2 compile option, C4244 warnings. #3489.
  • I confirmed that the issue reproduces in CI before fixing: https://github.com/embg/zstd/actions/runs/4147168689/jobs/7173726044#step:5:9
• Fix an incorrect MSVC 2019 compiler warning
• Remove a deprecated MSVC 2022 option (context), which was triggering a warning.
• Add /warnaserror to our msbuild CI jobs so we don't have these issues in future releases.

[embg]

It looks like my second commit, adding /warnaserror (the msbuild equivalent of -Werror), exposed a warning in the MSVC 2019 build. Will investigate ASAP.

[embg]

The MSVC 2019 build warnings were introduced by #3449. The errors are all caused by memcpy operations from BYTE const * * to BYTE const * *. The compiler incorrectly believes the const qualifiers don't match.

This warning doesn't show up in the MSVC 2022 build, so I think it is a bug in MSVC 2019.

Example warning (which is an error now that we have /warnaserror): https://github.com/facebook/zstd/actions/runs/4147381724/jobs/7174208209#step:4:207

Fixed by adding void* casts to the destination of each offending memcpy.