Mark System.Threading.Thread ResetAbort as Obsolete

[mdh1418]

It was recognized in #41892 that System.Threading.Thread ResetAbort throws PlatformNotSupportedException everywhere and should be marked as Obsolete.

[GrabYourPitchforks]

I've marked this ready for review since it's very straightforward. Recommend reusing the SYSLIB0006 (Thread.Abort is obsolete) code for this.

[terrajobst]

Video

• We believe it makes sense to reuse the existing diagnostic ID

namespace System.Threading
{
    public sealed class Thread
    {
        // Obsoleted in .NET 5:
        //[Obsolete(DiagnosticId = "SYSLIB0006")]
        //public void Abort();
        //[Obsolete(DiagnosticId = "SYSLIB0006")]
        //public void Abort(object stateInfo);
        [Obsolete(DiagnosticId = "SYSLIB0006")]
        public static void ResetAbort();
    }
}