fix(slide-toggle): clear name from host node

Along the same lines as #15422 and #15368. Clears the static `name` attribute from the slide toggle's host node in order to prevent both the underlying input and the host from showing up in `document.getElementsByName` or `By.name`.

src/lib/slide-toggle/slide-toggle.spec.ts

@@ -1031,6 +1031,12 @@ describe('MatSlideToggle with forms', () => {
 
       expect(testComponent.isSubmitted).toBe(true);
     });
+
+    it('should clear static name attribute from the slide toggle host node', () => {
+      const hostNode = fixture.nativeElement.querySelector('.mat-slide-toggle');
+      expect(inputElement.getAttribute('name')).toBeTruthy();
+      expect(hostNode.hasAttribute('name')).toBe(false);
+    });
   });
 
   describe('with model and change event', () => {

src/lib/slide-toggle/slide-toggle.ts

@@ -87,6 +87,7 @@ export const _MatSlideToggleMixinBase:
     'class': 'mat-slide-toggle',
     '[id]': 'id',
     '[attr.tabindex]': '-1', // Needs to be `-1` so it can still receive programmatic focus.
+    '[attr.name]': 'null',
     '[class.mat-checked]': 'checked',
     '[class.mat-disabled]': 'disabled',
     '[class.mat-slide-toggle-label-before]': 'labelPosition == "before"',