First of all. It’s still not recommended to use it. We know that people coming from vst2 like to use it, because it uses the same hack friendly way of coding as vst2. So a clean separation between audio processor and edit controller is the recommended way of writing a VST3 plug-in.
But to answer you question, you can have a look in the SDK source code. The method PlugProvider::setupPlugin implements the way how a plug-in audio processor and edit controller is created. All provided host examples in the SDK support this kind of plug-in (like the validator).
I think all VST3 hosts will support single component plug-ins beside Cubase before 4.2.