mark Windows-specific APIs as such (#39265)

mark Windows-specific APIs as such (#39265)

* move all OSPlatformAttributes to a single file so they can be easily referenced in < .NET 5 libraries

* Adds System.Runtime.Versioning*Platform* annotation attributes to < .NET 5 builds

* introduce MinimiumSupportedWindowsPlatform

* introduce IsWindowsSpecific setting that adds MinimumOSPlatform attribute for Windows Specific libraries

* mark all Windows-specific libraries as such

* annotate Windows-specific System.Console methods and properites

* annotate Windows-specific DpapiProtectedConfigurationProvider type

* annotate throwing Windows-specific APIs from System.Diagnostics.Process namespace

* annotate throwing Windows-specific APIs from System.IO.MemoryMappedFiles namespace

* annotate Windows-specific APIs from System.IO.Pipes namespace

* the new attributes should support enums

* annotate Windows-specific APIs from HttpListenerTimeoutManager class

* annotate Windows-specific APIs from System.Net.Sockets namespace

* annotate Windows-specific APIs from System.Runtime.InteropServices namespace

* annotate Windows-specific APIs from System.Security.Cryptography.Csp namespace

* annotate Windows-specific APIs from System.Security.Cryptography.X509Certificates namespace

* annotate Windows-specific APIs from System.Threading namespace

* address code review feedback: dont introduce new constants, reuse existing SYSTEM_PRIVATE_CORELIB

* code review: import the namespace, simplify the attribute name

* add missing Socket.DuplicateAndClose and Socket(SocketInformation)

* fix the test name (it does not throw)

* add missing DriveInfo.set_VolumeLabel

* add System.IO.FileSystem File Encrypt and Descrypt methods

* simplify the < .NET 5 check

* enable nullable in explicit way as it's not enabled in all the projects where this file is included

* include platform attributes in projects that ask for it in explicit way

* set IncludePlatformAttributes to true for projects that include files from other projects

* use suggestions from Viktor and Santi

Co-authored-by: Viktor Hofer <viktor.hofer@microsoft.com>