Improve type safety

[vgvassilev]

I don't think so. :) And there seems to be a real benefit there to prevent crashes.

struct ScopeCursor {
    void* fDecl;
};

Certain operations that can be performed on Decls and other on Types. We have interface GetScopeFromType and GetTypeFromScope if we need to convert but I'd prefer to have these explicit. This is more aligned to the underlying compiler API. I'd be happy if we had a special opaque entity for both. Eg:

    typedef ScopeCursor* CppScope_t;

    struct TypeCursor {
        void* fType;
        operator CppScope_t() { return GetScopeFromType(*this); }
    };

    typedef TypeCursor* CppType_t;

Here the compiler could enforce some checks if we try to call an interface with the unexpected parameter. We should look into better ways to strong typing as used here:
https://github.com/llvm/llvm-project/blob/4875e0670926b0a40ce0dd2c3d490b1866889f54/clang/include/clang-c/Index.h#L2243-L2247

Where the cursor can be classified to point to particular data type via an enum. Perhaps we could implement the former suggestion and extend it with the latter.