[API Proposal]: Mark BrowserInteropHelper/DynamicScriptObject as obsolete

[h3xds1nz]

Background and motivation

Even though XBAP is unsupported and all of the code inside is a dead code (#9855 and #9865), those classes weren't marked as obsolete during removal. Marking it as obsolete will help to developers migrating apps from .NET Framework, and will emit clear message/warnings.

API Proposal

namespace System.Windows.Interop;

+ [Obsolete(DiagnosticId = Obsoletions.XBAPDiagId)]
  public static class BrowserInteropHelper
  {
  }

+ [Obsolete(DiagnosticId = Obsoletions.XBAPDiagId)]
  public sealed class DynamicScriptObject : DynamicObject
  {
  }

Risks

There are only benefits.