NativeControlHost AvaloniaLocator

[workgroupengineering]

Allow access to services registered in AvaloniaLocator within NativeControlHost.

public class NativeControlHost: Control
{
 ...
  protected T? GetService<T>();
  protected T GetRequiredService();
}

Use case

When developing a cross platform control that needs to access native platform controls such as WebView, Camera, etc... normally a Service Locator or Dependency Injection Container is used. Since AvaloniaLocator was marked private in PR #11557, every third-party developer who needs to access native controls uses their own SL or IoC, which means the app can have different SLs or IoCs.

Other things

The API should not allow access to Avalonia's internal services unless private API access is enabled.