Move Windows builder to Visual Studio 2026

[teusbenschop]

• Let the installer install the VC++ 2026 redistributable.
• Test existing installer with the updated redistributable.
• Make it build under Visual Studio 2026.
• Test it on clean Windows 10.
• Test upgrading existing install on Windows 10.
• Test it on clean Windows 11.
• Test upgrading existing installation on Windows 11.