Fix DataTable crashes when its data is not a React primitive

[djhi]

Problem

When the record field data is not a React primitive (for instance an object which can happen often with guessers), the application crashes.

Solution

Make sure to call toString on the value we have for a record field.

How To Test

• Story: https://react-admin-storybook-88930fp7l-marmelab.vercel.app/?path=/story/ra-ui-materialui-list-datatable--non-primitive-data
• Unit tests

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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