Hide X char in popup close button [accessibility] (#11040)

Set the attribute aria-hidden to 'true' in popup close button in order to address accessibility as without this attribute, the X character is announced as 'multiplication' or 'times' when accessibility voice over is enabled.

src/ui/popup.js

@@ -534,6 +534,7 @@ export default class Popup extends Evented {
             this._closeButton = DOM.create('button', 'mapboxgl-popup-close-button', this._content);
             this._closeButton.type = 'button';
             this._closeButton.setAttribute('aria-label', 'Close popup');
+            this._closeButton.setAttribute('aria-hidden', 'true');
             this._closeButton.innerHTML = '×';
             this._closeButton.addEventListener('click', this._onClose);
         }