Implement attached type/property check

The goal of the attached type/property check is to catch instantiating multiple copies of the same attached property, e.g. instead of having multiple Theme.fooColor there should only be one and then <id>.Theme.fooColor should be used for other instances. This prevents the duplicate creation of attached objects.

This might make sense as an informational check outside of the controls context – on the other hand, it might also be something that the engine or at least the compilers can optimise.