users: Add "(guest)" to names for guest users.

This commit adds code to add "(guest)" to user names of guest
users in the following places -
- right sidebar
- user pills, including the pills in search suggestion typehaead
- typeaheads for user
- sender names in message feed
- user profile popover and modals.
- user name in not subscribed warning banner.

Note that the indicator is shown only if enable_guest_user_indicator
setting is set to true.

As a result of this change, we now translate "deactivated" text
shown in user pills for deactivated users.

Fixes part of #26700.

web/src/compose_validate.js

@@ -173,6 +173,7 @@ export function warn_if_mentioning_unsubscribed_user(mentioned, $textarea) {
                 can_subscribe_other_users,
                 name: mentioned.full_name,
                 classname: compose_banner.CLASSNAMES.recipient_not_subscribed,
+                should_add_guest_user_indicator: people.should_add_guest_user_indicator(user_id),
             };
 
             const new_row = render_not_subscribed_warning(context);