Support finding usage of types

[WebFreak001]

This probably improves massively in quality when #293 is implemented

should find all variable assignments, possibly also of type auto, e.g.

struct Foo // search for usage of `Foo`
{
}

//  v this should of course also be included
Foo foo()
{
}

void main()
{
    auto v = foo();
    //   ^ this is interesting
}

This can be used to enhance the accuracy of find references and implement finding members of structs and classes accurately.