[NUI] Fix CA1063

[NUI] Fix CA1063

- https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1063
- Every unsealed type that declares and implements the IDisposable interface must provide its own protected virtual void Dispose(bool) method. Dispose() should call Dispose(true), and the finalizer should call Dispose(false). If you create an unsealed type that declares and implements the IDisposable interface, you must define Dispose(bool) and call it. For more information, see Clean up unmanaged resources (.NET guide) and Dispose pattern.