Fix <FormDataConsumer> causes its children to flicker

[djhi]

Problem

Fixes #10415

Solution

Keep a stable reference to the children function

How To Test

• Story before the fix: https://react-admin-storybook-jis75yi0c-marmelab.vercel.app/?path=%2Fstory%2Fra-core-form-formdataconsumer--basic. Enter a title then select a user. Notice the flicker each time you change the user value. You might have to set a CPU throttle in your devtool to notice it.
• Story after the fix: https://react-admin-storybook-lyoclo2wi-marmelab.vercel.app/?path=%2Fstory%2Fra-core-form-formdataconsumer--basic

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why): can't find a way to unit test this
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

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