Better error message for missing fixture

[la10736]

Now we issue an error[E0433]: failed to resolve: use of undeclared type or module ...

Maybe we can use quote_span!{} in combination to check some fake field to report that the fixture function or annotation is missed.

Otherwise we can provide a good error by errors API at least in nightly

[la10736]

quote_spanned macro don't give a way to build custom error message and we cannot know if a fixture will be processed or not (by now we cannot know if it is already processed too). So we can investigate just nightly's error API.