unread: Stop accessing page_param.unread_msgs after init.

This adds a get_unread_message_count helper that returns the size of
unread_messages and replaces the usage of page_param.unread_msgs.count
elsewhere in the codebase.

Fixes #23334.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

static/js/navbar_alerts.js

@@ -14,6 +14,7 @@ import * as compose_ui from "./compose_ui";
 import {localstorage} from "./localstorage";
 import * as notifications from "./notifications";
 import {page_params} from "./page_params";
+import * as unread from "./unread";
 import * as unread_ops from "./unread_ops";
 import * as unread_ui from "./unread_ui";
 import * as util from "./util";
@@ -172,7 +173,7 @@ export function initialize() {
             rendered_alert_content_html: render_desktop_notifications_alert_content(),
         });
     } else if (unread_ui.should_display_bankruptcy_banner()) {
-        const unread_msgs_count = page_params.unread_msgs.count;
+        const unread_msgs_count = unread.get_unread_message_count();
         open({
             data_process: "bankruptcy",
             custom_class: "bankruptcy",

static/js/unread.js

@@ -517,6 +517,10 @@ export function get_unread_messages(messages) {
     return messages.filter((message) => unread_messages.has(message.id));
 }
 
+export function get_unread_message_count() {
+    return unread_messages.size;
+}
+
 export function update_unread_topics(msg, event) {
     const new_topic = util.get_edit_event_topic(event);
     const {new_stream_id} = event;

static/js/unread_ui.js

@@ -100,7 +100,7 @@ export function should_display_bankruptcy_banner() {
 
     const now = Date.now() / 1000;
     if (
-        page_params.unread_msgs.count > 500 &&
+        unread.get_unread_message_count() > 500 &&
         now - page_params.furthest_read_time > 60 * 60 * 24 * 2
     ) {
         // 2 days.