Cleanup comments and clang-formatting

[StephanTLavavej]

This is structured as a series of commits for easier reviewing. It addresses code review feedback from GH-2064 and is largely a followup to that toolset update's introduction of clang-format 12.

• Cite VSO-586813 "T^ is not allowed in a union" to address code review feedback.
• Improve clang-format to address code review feedback.
• Enable clang-format with literally no changes.
• Shrink // clang-format off regions, literally no changes.
• Enable clang-format with whitespace-only changes.
• Enable clang-format with // wrapping, only whitespace changes.
• Enable clang-format with // wrapping.
• Enable clang-format for improved formatting.
• Add spaces after // begins a comment.
• Detach switch comments.
• Drop unnecessary comments for unnamed parameters.

[barcharcraz]

today I learned about the // line wrapping thing in clang-format

[StephanTLavavej]

I'm mirroring this to an MSVC-internal PR. Please notify me if any further changes are pushed.