fix(avatar): fix avatar disabled for icon content (#30820)

Issue number: internal

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## What is the current behavior?
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- When Avatar has an icon as content and is disabled, the icon is above
the disabled layer.

## What is the new behavior?
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this PR. -->
- add avatar with icon on disabled state page;
- add avatar with icon on snapshots tests;
- change disable state to be the :after pseudo element avatar content;


## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

[state](https://ionic-framework-git-rou-12319-ionic1.vercel.app/src/components/avatar/test/states?ionic:theme=ionic)

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Co-authored-by: ionitron <[email protected]>

Author: JoaoFerreira-FrontEnd

core/src/components/avatar/avatar.ionic.scss

@@ -244,7 +244,7 @@
 
 // Avatar Disabled
 // --------------------------------------------------
-:host(.avatar-disabled)::before {
+:host(.avatar-disabled)::after {
   @include globals.border-radius(var(--border-radius));
   @include globals.disabled-state();
 }

core/src/components/avatar/test/states/avatar.e2e.ts

@@ -12,6 +12,9 @@ configs({ directions: ['ltr'], modes: ['ionic-md'] }).forEach(({ config, screens
         ` 
         <div id="container"> 
           <ion-avatar disabled> AV </ion-avatar>
+          <ion-avatar disabled>
+            <ion-icon name="person-outline"></ion-icon>
+          </ion-avatar>
           <ion-avatar disabled>
             <img src="/src/components/avatar/test/avatar.svg" />
           </ion-avatar>

core/src/components/avatar/test/states/avatar.e2e.ts-snapshots/avatar-disabled-ionic-md-ltr-light-Mobile-Chrome-linux.png

@@ -25,6 +25,9 @@
       <ion-content>
         <h3>Disabled</h3>
         <ion-avatar disabled>AV</ion-avatar>
+        <ion-avatar disabled>
+          <ion-icon name="person-outline"></ion-icon>
+        </ion-avatar>
         <ion-avatar disabled>
           <img src="/src/components/avatar/test/avatar.svg" />
         </ion-avatar>