fix(material): remove usage of form-field deep import path

[AmGarera]

Adding a bug fix for an error I had run into when using Material Formly where the import was one level too deep.

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[aitboudad]

Thank you @AmGarera!

[aitboudad]

This PR has been released as part of v6.0.0-rc.0 release.

Please let us know, in case you are still encountering a similar issue/problem.
Thank you!