Upgrade to 3.0.0-preview4-19216-03

[Behnam-Emamian]

Hi

I try to update this project to 3.0.0-preview4-19216-03 but I have faced this error:
var engine = RazorProjectEngine.Create(BlazorExtensionInitializer.DefaultConfiguration, fileSystem, b =>
{
BlazorExtensionInitializer.Register(b);
});

BlazorExtensionInitializer is gone!!! :-\

and I dont know how can I replace it with new version.