fix(radio): clear names from host nodes

Along the same lines as angular#15368. Clears the `name` from the host node of the radio button and radio group, because they end up being forwarded to the underlying `input` and can cause double results when using something like `getElementsByName`.

src/material/radio/radio.spec.ts

@@ -65,6 +65,11 @@ describe('MatRadio', () => {
       }
     });
 
+    it('should clear the name attribute from the radio group host node', () => {
+      expect(groupInstance.name).toBeTruthy();
+      expect(groupDebugElement.nativeElement.getAttribute('name')).toBeFalsy();
+    });
+
     it('should coerce the disabled binding on the radio group', () => {
       (groupInstance as any).disabled = '';
       fixture.detectChanges();
@@ -727,6 +732,10 @@ describe('MatRadio', () => {
       expect(seasonRadioInstances.every(radio => radio.color === 'accent')).toBe(true);
     });
 
+    it('should clear the name attribute from the radio host node', () => {
+      expect(radioDebugElements.every(el => !el.nativeElement.getAttribute('name'))).toBe(true);
+    });
+
   });
 
   describe('with tabindex', () => {

src/material/radio/radio.ts

@@ -93,6 +93,7 @@ export class MatRadioChange {
   host: {
     'role': 'radiogroup',
     'class': 'mat-radio-group',
+    '[attr.name]': 'null',
   },
 })
 export class MatRadioGroup implements AfterContentInit, ControlValueAccessor {
@@ -346,6 +347,7 @@ const _MatRadioButtonMixinBase:
     // Needs to be -1 so the `focus` event still fires.
     '[attr.tabindex]': '-1',
     '[attr.id]': 'id',
+    '[attr.name]': 'null',
     // Note: under normal conditions focus shouldn't land on this element, however it may be
     // programmatically set, for example inside of a focus trap, in this case we want to forward
     // the focus to the native element.