Investigate if FolderBrowserDialog.AutoUpgradeEnabled property is obsolete on win7+

[Tanya-Solyanik]

• .NET Core Version: 3.0
• Have you experienced this same bug with .NET Framework?: N/A

As far as I understand, this property auto-upgrades the XP dialog to the Vista dialog. We need to double check if this is relevant on the OSs that Core ships on. Once this is understood, we need to update the docs - https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Windows.Forms/FolderBrowserDialog.xml and consider making this property obsolete.

Supported OSs: https://github.com/dotnet/core/blob/master/release-notes/3.0/3.0-supported-os.md

OS	Version	Architectures	Notes
Windows Client	7 SP1+, 8.1	x64, x86
Windows 10 Client	Version 1607+	x64, x86
Nano Server	Version 1803+	x64, ARM32
Windows Server	2012 R2 SP1+	x64, x86

[RussKie]

Related https://github.com/dotnet/winforms/issues/1640

[JeremyKuhne]

Using the old (pre Vista) file browser dialog is still supported. This isn't worth spending time on.