fix(Form): conditionally type form data via transform prop

[tankosinn]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

• Introduce the FormData<S, T> conditional type helper.
• Update the onSubmit prop and submit event payload to use FormData<S, T>.
• Add a T generic to the internal _validate function and to Form.validate() to respect the transform option when inferring the form schema.
• Use the S (FormSchema) generic for Form instead of I (InferInput<S>) enabling schema inference via FormData<S, T>.
• No runtime behavior changes; all changes are type-only.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@4188

commit: f25ca8b

[romhml]

Thanks @tankosinn :)