bug(MatRadioButton): The `required` attribute is used on a radio button

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

When used in a radio group, the `required` attribute is used on a radio button. All the radio buttons under the group have `required` attributes. This attribute should not be used on individual radio buttons, because that creates illogical meta-data, which may be confusing for assistive technology users. It's not the individual controls that are required, it's the group as a whole that must have one choice made from it.

Code reference: https://source.corp.google.com/piper///depot/google3/third_party/javascript/angular_components/src/material/radio/radio.ts;l=250-257;bpv=1;bpt=1

### Reproduction

StackBlitz link:
Steps to reproduce:
1.
2.

### Expected Behavior

When a radio button is used inside a radio group, if the group is required and does not have a default selection, then add `aria-required="true"` to the wrapping element, not `aria-required/required` to the individual controls. We can leave it unchanged when a radio button is used outside a radio group, though I am unsure if that is a valid use case.

### Actual Behavior

The `required` attribute is applied to each radio button in a group.

### Environment

- Angular:
- CDK/Material:
- Browser(s):
- Operating System (e.g. Windows, macOS, Ubuntu):

Start in radio.ts around the referenced lines where the required attribute is applied, and inspect the radio-group handling nearby. Verify the behavior for grouped and standalone radio buttons, then run the relevant radio component tests; done means a required group exposes aria-required on its wrapper without applying required or aria-required to each child control.

Written by the indexing model from the issue text.