Accessibility: Improve the way emojis are announced by screen readers.

Adds an ARIA `role="img"` to the emojis markup in the front end. While the ARIA role is technically redundant, it helps Safari and VoiceOver to properly announce the emojis as "image". Without the role, they announce a generic "group" role.
Tested with Safari 12.1.1 / VoiceOver 9.

Props pento.
See #37486.


git-svn-id: https://develop.svn.wordpress.org/trunk@45726 602fd350-edb4-49c9-b593-d223f7449a82

src/js/_enqueues/wp/emoji.js

@@ -253,6 +253,11 @@
 
 					return ''.concat( options.base, icon, options.ext );
 				},
+				attributes: function() {
+					return {
+						role: 'img'
+					};
+				},
 				onerror: function() {
 					if ( twemoji.parentNode ) {
 						this.setAttribute( 'data-error', 'load-failed' );