Win10 baseline: Drop support for Win8.1 / Server 2012 R2

[StephanTLavavej]

🗺️ Overview

• Followup to Win8 baseline: Drop support for Win7 / Server 2008 R2 #5432.
• The impact on the GitHub side is minimal, but I'll be adding more significant MSVC-internal changes when mirroring.
  • Together, the removal of Win7, Win8, and Win8.1 support will shrink the VCRedist executables by 6.7 MB each.
• Works towards Support for Win7 / Server 2008 R2 through Win8.1 / Server 2012 R2 is DOOMED #4858.
  • I'll need to get our documentation updated.
• This will not be backported.
  • For the rest of its lifecycle, VS 2022 17.14 will support Win7, Win8, and Win8.1.

This removal was formally approved today (internal VSO-2441848). We are fully aware that their counterparts Server 2012 and Server 2012 R2 are entering their final year of ultra-extended super-premium paid support.

📜 Changelog

• The STL no longer supports targeting Windows 7 / Server 2008 R2, Windows 8 / Server 2012, and Windows 8.1 / Server 2012 R2.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.