Support dependent fields in internals

[ddobrev]

We need to handle cases such as:

template
class Whatever
{
T Foo;
}

class Bar
{
Whatever W;
}

In here, Foo is a dependent field. We need to represent it in Internals as an int. One of the approaches is generating a separate internal struct per template specialisation.

[tritao]

Another possible approach is to generate the dependent fields recursively in the internal definitions, without having to generate an explicit Internal struct for each template specialization, though long-term, that approach would be better, since we could also generate a proper class for it, to be able to access template specializations directly in C#. That's a bit tricky too, and it might be better to spend the effort on getting the cross-platform C++/CLI working.

[ddobrev]

Dependent fields in internals are actually impossible to support. Structures with native layouts cannot be generic so we can only use separate structures per specialisation which we already do.