Resolve ForwardRef on Field.outer_type_

[JacobHayes]

Change Summary

When resolving ForwardRefs, the Field.outer_type_ is not resolved, only Field.type_. This PR updates update_field_forward_refs to resolve both attributes, while still only calling Field.prepare once.

Field.outer_type_ can be a nested object (eg: List[str], etc), but I only check if the entire annotation is a ForwardRef for simplicity. This should cover most cases, namely:

• all from __future__ import annoations annotations
• manually stringized annotations as long as the whole annotation is stringized (eg: "List[RecursiveType]" will be resolved, List["RecursiveType"] will not)

I think I've seen other instances where ForwardRefs inside nested types aren't full resolved, so 🤞 this is fine for now.

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[JacobHayes]

I think this is ready, please review 🙏

[samuelcolvin]

thanks so much.