Refactor IDataConsumer for the TestHostController

[MarcoRossignoli]

Make the IDataConsumer registration symmetric in both model. Historically we added a way to have data consumer inside the test host for "questionable" trx needs.

So we were foreaching the extension and in case of IDataConsumer implementation we were adding as listener to the IMessageBus to allow for instance the codecov old version to push the file that the trx could take to put inside the report self.

Nowadays where we run the trx and cc in-process this is mostly non needed but anyway we have a feature to collect artifacts inside the test host controller to "add attachments" if someone there is producing something.
This is an "hidden" and not documented behavior used only by our trx extension. So it's fine to update and make it coherent with the rest, but won't be exposed yet and most probably never. I don't know if we will never have reason to do it. The logic is that outside you push artifacts and stop, like the current VSTest logger, so I would not expose this feature but for now I'll internalize the method only to keep the current trx behavior.

I'll update the trx extension as soon as we'll flow this there.

cc: @Evangelink wait the trx update on the other side before to ship