What does this PR do?

Fixes an issue where if you tab beyond a formField and focus doesn't move to another element the node passed to withinDropPortal is undefined, resulting in the following error:

What testing has been done on this PR?

Tested with the following story:

import React from 'react';

import { Box, DateInput, Form, FormField } from 'grommet';

export const Test = () => (
  <Box fill align="center" justify="center">
    <Form validate="blur">
      <FormField label="Enter a date">
        <DateInput format="mm/dd/yyyy-mm/dd/yyyy" />
      </FormField>
    </Form>
  </Box>
);

export default {
  title: 'Input/Form/Test',
};

How should this be manually tested?

Using the above story tab past the DateInput

Do Jest tests follow these best practices?

• screen is used for querying.
• The correct query is used. (Refer to this list of queries)
• userEvent is used in place of fireEvent.
• asFragment() is used for snapshot testing.

Any background context you want to provide?

What are the relevant issues?

Screenshots (if appropriate)

Do the grommet docs need to be updated?

No

Should this PR be mentioned in the release notes?

Yes

Is this change backwards compatible or is it a breaking change?

Backwards compatible