fix(material/dialog): dialog name not read by screenreader on macos using chrome or firefox

Updates fix for Angular Components Dialog issue where the dialog name
is not being read by the screenreader when specifically using macos
(and potentially ios) screenreader when using chrome or firefox
browsers. Removes unused commented out code and includes ios as part
of the logic to call  _getDialogName().

Fixes b/274674581

Author: essjay05

src/material/dialog/dialog-container.ts

@@ -97,8 +97,6 @@ export class MatDialogContainer
     : 0;
   /** Current timer for dialog animations. */
   private _animationTimer: ReturnType<typeof setTimeout> | null = null;
-  /** Platform Observer */
-  // private _userAgentSubscription = Subscription.EMPTY;
   private _getWindow(): Window {
     return this._document?.defaultView || window;
   }
@@ -169,7 +167,7 @@ export class MatDialogContainer
 
   private _setAriaLabel = (): void => {
     const os = this._getUserPlatform();
-    if (os === 'macos') {
+    if (os === 'macos' || os === 'ios') {
       this._getDialogName();
     }
     return;