Async validators

[vlukashov]

• validator() functions can by asynchronous.
• The state of a form or a single field has a property to signal that an async validation is in progress. Async and sync validators can be combined.

const isAvailableName = async (value) => {
  const response = await fetch(`/validate/name/${encodeURIComponent(value)}`);
  const result = await response.json();
  if (result.error) {
    return `Please pick another name. '${value}' is not available.`;
  }
};