[Auth] Add aria-hidden='true' attribute to embedded iframe (#5633)

* Add aria-hidden='true' attribute to embedded iframe

* Add changeset

Author: sam-gc

.changeset/olive-coats-deliver.md

@@ -0,0 +1,5 @@
+---
+"@firebase/auth": patch
+---
+
+Add the attribute `aria-hidden="true"` to the embedded iframe

packages/auth/src/platform_browser/iframe/iframe.test.ts

@@ -84,7 +84,8 @@ describe('platform_browser/iframe/iframe', () => {
         top: '-100px',
         width: '1px',
         height: '1px'
-      }
+      },
+      'aria-hidden': 'true',
     });
     expect(iframeSettings.dontclear).to.be.true;
   });

packages/auth/src/platform_browser/iframe/iframe.ts

@@ -37,7 +37,8 @@ const IFRAME_ATTRIBUTES = {
     top: '-100px',
     width: '1px',
     height: '1px'
-  }
+  },
+  'aria-hidden': 'true'
 };
 
 // Map from apiHost to endpoint ID for passing into iframe. In current SDK, apiHost can be set to