Docs: add Formisch to the form libraries section of the forms guide

[fabian-hiller]

🙋 Documentation Request

The forms guide shows how to integrate React Aria components with React Hook Form and Formik. I'd like to contribute an example for Formisch, a schema-based, headless form library I maintain. It validates with a Valibot schema, infers all types from it, and works with React Aria components via its render-prop Field component. Happy to open a PR to packages/dev/s2-docs/pages/react-aria/forms.mdx if there is interest.

🧢 Your Company/Team

Formisch (open source)

[yihuiliao]

Resolved in #10410