[FormLabel] [FormHelperText] classes keys

[Mangatt]

Even though [FormControl] provides context filled/focused/error/required, not all these keys are available in [FormLabel] and [FormHelperText] classes.

I believe that filled/focused/required keys should be available as well. It is valid use case to change Component styling based on it's internal state.

I know that it is possible to achieve similar functionality now (hijack MuiFormControl context or control Component state externally), but it's bit overkill since it's already been done once.

[oliviertassinari]

@Mangatt Would having #7633 solve your problem and remove the need for adding these extra classes?

[Mangatt]

Probably. But I still think that it should be available directly through classes prop, there's no reason to omit those keys.

[oliviertassinari]

@Mangatt I agree, feel free to work on it :)