inputValidator with Zod for FormData

[cjoecker]

Right now, the documentation suggests validating the formData by checking for an instance of it.
That requires extra logic to be built on every inputValidator and is not a great DX.

It would be great if the inputValidator checks if the data is an instanceof FormData and then it validates the FormData with zod as is done in zod-form-data

Then, we would be able to just have this also with the body as FormData and get a type safe result without extra wrapers:

// Body is FormData
export const createUser = createServerFn({ method: 'POST' })
  .inputValidator(UserSchema)
  .handler(async ({ data }) => {
    // data is fully typed and validated
    return `Created user: ${data.name}, age ${data.age}`
  })