Add a further Link field formatter, or extend the existing one, which is able to choose another micon field as icon source

I thought about this feature again, and while there are cases where this approach makes sense, the example given (button paragraph) works well with the existing Micon link formatter.

So let's postpone this for now.

I think this is a duplicate of ✨ Create a micon + linkit (and micon + linkit + link_attributes) submodule Needs review