[Microsoft Generator CSharp] Do we still need the ApiTypes in MGC?

[ArcturusZhang]

Describe the issue or request

The position of ApiTypes is awkward because it is not really enforced and there is no way to enforce that we have to use the information in it.
For the type definition part, could we use the TypeFactory to define the types of some specific roles?
And for the XXXMethodName part, I think we could always put those part in a suitable place in our expressions.