Add missing enum & ctor for PackedVector4Array implementation

[Naros]

@dsnopek I think this may have been overlooked in #1456

[dsnopek]

Thanks!

However, this only appears to update variant.hpp - shouldn't the implementations for these methods need to be added to variant.cpp as well?

[Naros]

Thanks!

However, this only appears to update variant.hpp - shouldn't the implementations for these methods need to be added to variant.cpp as well?

Ya it does, fixed the PR.

[dsnopek]

Thanks!

I haven't tested it, but the code looks good to me. Assuming this passes CI, I think it's good to go :-)