Add platform-specific attributes (#38604)

Add platform-specific attributes (#38604)

* Add platform-specific attributes

Spec https://github.com/dotnet/runtime/issues/33331

* Convert to xml doc

* Update src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/MinimumOSAttribute.cs

Co-authored-by: Jeremy Barton <jbarton@microsoft.com>
* Update src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ObsoletedInPlatformAttribute.cs

Co-authored-by: Jeff Handley <jeffhandley@users.noreply.github.com>
* Address code review

* Add to ref assembly, test and fix build errors

* Fix spacing, revert unwanted changes

* Namespace was wrong, updated

Co-authored-by: Jeremy Barton <jbarton@microsoft.com>
Co-authored-by: Jeff Handley <jeffhandley@users.noreply.github.com>
Co-authored-by: Buyaa Namnan <bunamnan@microsoft.com>