Account for deleted forms when encryption is enabled for project

When [managed encryption](https://docs.getodk.org/central-encryption/) is enabled for a project, a new, encrypted version of each form is created. However, this process skips deleted forms (forms in the trash). That means that if a deleted form is undeleted after encryption is enabled, the form will not be encrypted. Specifically, the following sequence is possible:

- Create a project.
- Create and publish a form.
- Delete the form.
- Enable encryption for the project.
- Undelete the form.
- Observe that the form is not encrypted.

Here are two different approaches that we could consider:

1. Immediately create new, encrypted form versions even for deleted forms.
2. Don't change deleted forms, but if/when a form is undeleted, create a new, encrypted form version then.