fix emails in chat (#10912)

* additional regex checks to ignore the <tag attribute="content">

* extract highlightUsers method - add test

* refactor highlight regex

* refactor the regex without `lookbehind`

* remove unneeded regex

website/client/libs/highlightUsers.js

@@ -0,0 +1,18 @@
+export function highlightUsers (text, userName, displayName) {
+  const findAnyMentionRegex = '@[\\w-]+(?:\\b)';
+
+  const atRegex = new RegExp(`${findAnyMentionRegex}`, 'gi');
+  const currentUser = [`@${userName}`, `@${displayName}`];
+
+  if (atRegex.test(text)) {
+    text = text.replace(atRegex, match => {
+      if (currentUser.includes(match)) {
+        return `<span class="at-highlight at-text">${match}</span>`;
+      }
+
+      return `<span class="at-text">${match}</span>`;
+    });
+  }
+
+  return text;
+}