Better support for exactOptionalPropertyTypes: true

[jakubmazanec]

Describe the bug and the expected behavior

When TypeScript compiler option exactOptionalPropertyTypes is set to true, you cannot pass undefined as a value to an object property that is marked as optional. While IMO very useful option, it can lead to bad DX, because it can cause TypeScript errors:

import {useForm} from '@conform-to/react';

type CustomComponentProps = {
  onSubmit?: Parameters<typeof useForm>[0]['onSubmit'] | undefined;
}

let CustomComponent = ({onSubmit}: CustomComponentProps ) => {
  let [form] = useForm({
    onSubmit // error here, because `onSubmit` prop can be `undefined`
  });

 // rest of the component
}

I therefore prefer that "input" types (like function parameters, properties in options objects, etc.) have explicit undefined added to them; e.g. here I would like to have this:

export type FormOptions<
	Schema extends Record<string, any> = any,
	FormError = string[],
	FormValue = Schema,
> = BaseFormOptions<Schema, FormError, FormValue> & {
	/**
	 * A function to be called before the form is submitted.
	 */
	onSubmit?: ((
		event: FormEvent<HTMLFormElement>,
		context: ReturnType<
			BaseFormContext<Schema, FormError, FormValue>['submit']
		>,
	) => void) | undefined; // here I added explicit `undefined` to the type ⚠️
};

Would it be possible to add undefined to all input types? Thank you.

Conform version

v1.1.5

Steps to Reproduce the Bug or Issue

What browsers are you seeing the problem on?

No response

Screenshots or Videos

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Additional context

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