What does this PR do?

Fixes an issue in SelectMultiple where objects are not being correctly compared. This PR removes array function instances such as indexOf and includes which don't work well for arrays containing objects.

Note: marking as a draft, I still need to add jest tests

Where should the reviewer start?

See the getOptionIndex and arrayIncludes functions added in the util file.

What testing has been done on this PR?

Tested with existing storybook stories and the following story (see codesandbox to see before and after):

import React, { useState } from 'react';

import { SelectMultiple } from '../SelectMultiple';
const options = [
  { fieldType: 'SYSTEM', value: 'abc', display: 'ABC', other: 123 },
  { fieldType: 'SYSTEM', value: 'xyz', display: 'XYZ', other: 456 },
];
export const Test = () => {
  const [value, setValue] = useState([
    {
      fieldType: 'SYSTEM',
      value: 'abc',
      display: 'ABC',
      other: 123,
    },
  ]);
  return (
    <SelectMultiple
      showSelectedInline
      labelKey="display"
      valueKey="value"
      options={options}
      value={value}
      onChange={({ value }) => setValue(value)}
    />
  );
};

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

How should this be manually tested?

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?

Closes #6395

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