fix(radio-button): underlying input not respecting value binding

Currently a `mat-radio-button` does not respect the value binding that has
been set on the radio-button.

This is not ideal because in most cases the value is a primitive that can
be set as `value` for the underlying input element in order to ensure that
proper `FormData` can be retrieved when the form gets submitted.

Currently the form data will always have `on` as value because the selected
radio-button does not pass-through the value to the underlying input.

Author: devversion

src/material/radio/radio.html

@@ -21,6 +21,7 @@
         [disabled]="disabled"
         [tabIndex]="tabIndex"
         [attr.name]="name"
+        [attr.value]="value"
         [required]="required"
         [attr.aria-label]="ariaLabel"
         [attr.aria-labelledby]="ariaLabelledby"

src/material/radio/radio.spec.ts

@@ -657,6 +657,11 @@ describe('MatRadio', () => {
       expect(radioInstance.required).toBe(true);
     });
 
+    it('should add value attribute to the underlying input element', () => {
+      expect(fruitRadioNativeInputs[0].getAttribute('value')).toBe('banana');
+      expect(fruitRadioNativeInputs[1].getAttribute('value')).toBe('raspberry');
+    });
+
     it('should add aria-label attribute to the underlying input element if defined', () => {
       expect(fruitRadioNativeInputs[0].getAttribute('aria-label')).toBe('Banana');
     });