Support validation errors on checkboxes and radio buttons

[anthony-o]

Bug, feature request, or proposal:

Support validation errors in checkboxes and radio buttons. For instance, displaying radio button labels in red when required mat-radio-group was not filled-in.

What is the expected behavior?

This stackblitz should display red label on the radio buttons when clicking on "Submit".
It contains one required mat-radio-group (with multiple mat-radio-buttons in it) and one required input.

What is the current behavior?

Currently, only the text input in the mat-form-field is correctly displayed in red when clicking on Submit.

What are the steps to reproduce?

Providing a StackBlitz reproduction is the best way to share your issue.

StackBlitz starter: https://goo.gl/wwnhMV

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 5.2.0 as well as 6.0.0

[Mr-Eluzive]

I think it would be useful feature and if no one mind then I can try do something with this. But I think it also require some work on #7891 because right now there is no label.

[josephperrott]

Duplicate of #7891

[andresroberto]

#7891 was about using checkbox and radio buttons inside a form-field. This issue is about supporting error highlighting in checkboxes and radio buttons, not necessarily by using checkbox and radio buttons inside a form-field. Therefore, even though they are related, I don't think this is a duplicate. And it would be awesome to have required radio buttons get red when trying to submit them empty.

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