Add debugging information to resolve warning

[felix-hilden]

From #105: it could be helpful to add the expected (parsed) location of a type to the resolve warning for users. In the linked issue it's not really clear whether autolink has parsed the correct target and not resolved, or failed altogether, or if the fault is in the generated documentation instead. Displaying the expected location would allow users to verify that a sequence of statements has been parsed correctly and thus narrow down the cause or provide more information when submitting a bug report.

We provide the key in missing inventory warnings. This would be akin to that, except that we don't actually know the key so we have to take a step back.