Better support for non-function type aliases

[yanok]

Mockito currently just ignores non-function type aliases and works with the target type directly. Which is usually fine, unless the target type is private. We added support for mocking non-function type aliases some time ago, we should probably add support for referencing them properly as well.

This probably boils down to moving the if (type.alias != null) branch out of if (type is FunctionType) branch to the top-level of _typeReference method. Not sure what analyzer gives us for the nested aliases case though... Is it possible to step through the aliases one by one? That needs to be checked.