Bug Report

Ionic version:
[ ] 4.x
[x] 5.x

Current behavior:
Screen readers read content behind overlays if is present more than 1 overlay and, after closing the last overlay, the aria-hidden applied on the ion-router-outlet component is removed despite the first modal is already present.

Expected behavior:
if I open another overlay (inside an overlay for example) the screen reader doesn't have to read the hidden overlay and if I close the second overlay, the ion-router-outlet component must have the attribute aria-hidden if an overlay is present

Steps to reproduce:

open first overlay -> open second overlay from first overlay

A sample application via GitHub
https://stackblitz.com/edit/ionic-bug-overlays

Ionic info:

Ionic:
   Ionic CLI                     : 6.16.1
   Ionic Framework               : @ionic/angular 5.6.9
   @angular-devkit/build-angular : 0.1100.7
   @angular-devkit/schematics    : 11.0.7
   @angular/cli                  : 11.0.7
   @ionic/angular-toolkit        : 3.1.1
Cordova:
   Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms : android 9.0.0, ios 5.1.1
   Cordova Plugins   : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 5.0.0, (and 41 other plugins)
Utility:
   cordova-res                          : not installed globally
   native-run (update available: 1.4.0) : 1.2.2
System:
   Android SDK Tools : 26.1.1
   ios-deploy        : 1.10.0
   ios-sim           : 8.0.2
   NodeJS            : v12.19.0 (/usr/local/bin/node)
   npm               : 6.14.13
   OS                : macOS Big Sur
   Xcode             : Xcode 12.5 Build version 12E262