That class is intended to be used only for classes in the javaee/impl project, that's why it is not visible for other projects. What do you need in it that can't be solved by extending from AbstractProjectCommand?
my question is a follow-up to my former thread Developing a simple Add-on
However I've just followed your advice and checked the method getSelectedProject is also available by extending extending from AbstractProjectCommand
ServletFacet<?> servletFacet = getSelectedProject(context).getFacet(ServletFacet.class);
So good, thanks for the clarification!