fix(Accordion): use the hidden attribute

The edge compatibility issue is standard edge behaviour that's quickly
fixed with user css, provided compat in our example

Author: synecdokey

src/css/fancy-example.css

@@ -42,7 +42,7 @@
     transform: rotate(45deg);
 }
 
-.accordion *[data-hidden] {
+[hidden] {
     display: none;
 }
 

src/helpers/AccordionStore.ts

@@ -5,7 +5,7 @@ export interface InjectedPanelAttributes {
     'aria-hidden': boolean | undefined;
     'aria-labelledby': string;
     id: string;
-    'data-hidden': boolean | undefined;
+    hidden: boolean | undefined;
 }
 
 export interface InjectedHeadingAttributes {
@@ -92,7 +92,7 @@ export default class AccordionStore {
             'aria-hidden': this.allowMultipleExpanded ? !expanded : undefined,
             'aria-labelledby': this.getButtonId(uuid),
             id: this.getPanelId(uuid),
-            'data-hidden': expanded ? undefined : true,
+            hidden: expanded ? undefined : true,
         };
     };