[API Proposal]: Mark BrowserInteropHelper/DynamicScriptObject as obsolete

### 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

```diff
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.