refactor(cdk/dialog): account for top-level popovers

Updates the logic that sets `aria-hidden` on top-level elements to account for popovers.

Author: crisbeto

src/cdk/dialog/dialog.ts

@@ -401,7 +401,8 @@ export class Dialog implements OnDestroy {
           sibling !== overlayContainer &&
           sibling.nodeName !== 'SCRIPT' &&
           sibling.nodeName !== 'STYLE' &&
-          !sibling.hasAttribute('aria-live')
+          !sibling.hasAttribute('aria-live') &&
+          !sibling.hasAttribute('popover')
         ) {
           this._ariaHiddenElements.set(sibling, sibling.getAttribute('aria-hidden'));
           sibling.setAttribute('aria-hidden', 'true');