feat(toggle): add --border-radius and --handle-border-radius variables (#20141)

core/src/components/toggle/test/basic/index.html

@@ -70,6 +70,11 @@
           <ion-label>Button w/ right side default icon, really long text that should ellipsis</ion-label>
           <ion-icon name="information-circle" slot="end"></ion-icon>
         </ion-item>
+        
+        <ion-item>
+          <ion-label>Custom</ion-label>
+          <ion-toggle slot="start" style="--border-radius: 0px;--handle-border-radius: 0px;" checked></ion-toggle>
+        </ion-item>
 
       </ion-list>