style(runtime): set aria-hidden to true to the splite for the accessibility reason

The sprite is inserted immediately below the body element, but all elements immediately below the
body must be either landmarks or insivible for the blind users. Please see this document for the
detail. https://dequeuniversity.com/rules/axe/3.2/region?application=axeAPI

Author: Hiroaki KARASAWA

runtime/browser-sprite.js

@@ -11,7 +11,12 @@ let sprite;
 if (isSpriteExists) {
   sprite = window[spriteGlobalVarName];
 } else {
-  sprite = new BrowserSprite({ attrs: { id: spriteNodeId } });
+  sprite = new BrowserSprite({
+    attrs: {
+      id: spriteNodeId,
+      'aria-hidden': 'true'
+    }
+  });
   window[spriteGlobalVarName] = sprite;
 }