Make RenderingProcess a mixin

Current the AnnotationDrivenProcessFactory looks for methods named "invertQuery" or "invertGridGeometry" and if found calls the Process as a RenderingProcess (via InvokeMethodRenderingProcess).

It would be nice to surface the invertQuery and invertGridGeometry methods as an interface, for better documentation,
One way to do this is to change the RenderingProcess interface to be a mixin, rather than extending Process. Then it can be used for all rendering transformation processes (including anno-driven ones), and the AnnotationDrivenProcessFactory could simply check for this interface to decide how to wrap the process.