Accessibility: Taxonomy: When a new category or tag is being added, show a spinner and noop the button to avoid multiple requests.

Props andg, afercia, guddu1315, SergeyBiryukov.
Fixes #47607.

git-svn-id: https://develop.svn.wordpress.org/trunk@45683 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/edit.css

@@ -1163,6 +1163,11 @@ p.popular-tags a {
 	text-decoration: underline;
 }
 
+#addtag .spinner {
+	float: none;
+	vertical-align: top;
+}
+
 #edittag {
 	max-width: 800px;
 }