[material-ui][RadioGroup] Apply classnames

[ZeeshanTamboli]

• I have followed (at least) the PR section of the contributing guide.

Fixes #41076

Preview: https://deploy-preview-41610--material-ui.netlify.app/material-ui/react-radio-button/

Rather than modifying the radio group classnames in the API documentation, I think the correct fix is to apply those classnames to the Radio Group component. The API documentation for Radio button CSS classes is correct.

Having both MuiFormGroup and MuiRadioGroup classes might not seem ideal, but it's consistent with other components like the Outlined Input, which has both MuiOutlinedInput and MuiInputBase related classnames. However, this does lead to an increase in bundle size.

If we decide to retain only the radio group related classes, two things need consideration:

• Removing form group related classnames would constitute a breaking change, which might be acceptable for version 6.
• We'd need to separate the Radio Group from Form Group. Although it's implementation would largely remain the same as Form Group, Radio Group wouldn't inherit from Form Group.

[mui-bot]

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[DiegoAndai]

Looks good to me 👍🏼

I wouldn't remove the FormGroup classes unless there's an issue with them. I don't think they bloat the component too much. We could open an issue to discuss it if you feel like it's necessary, but as you mention, it would have to remain consistent with other components.

[ZeeshanTamboli]

I also included tests.

I wouldn't remove the FormGroup classes unless there's an issue with them. I don't think they bloat the component too much. We could open an issue to discuss it if you feel like it's necessary, but as you mention, it would have to remain consistent with other components.

Alright, I am fine if it needs to be consistent.