Use SVG link arrows to avoid mobile emoji rendering

site/styles.css

@@ -1131,3 +1131,11 @@ kbd {
     margin-top: 7px;
   }
 }
+
+/* SVG external-link arrows avoid platform emoji presentation. */
+.link-arrow {
+  display: inline-block;
+  width: 1em;
+  height: 1em;
+  vertical-align: -0.125em;
+}