This commit adds non-archived group messages and `group_message_summary` notifications in the messages tab in the user menu. With this change, the messages tab in the user menu now includes 3 types of items:
1. Unread `private_message` notifications (notifications when you receive a reply in a PM)
2. Unread and read `group_message_summary` notifications (notifications when there's a new message in a group inbox that you track)
3. Non-archived personal and group messages
Unread `private_message` notifications are always shown first, followed by unread `group_message_summary` notifications, and then everything else (messages and read `group_message_summary` notifications) sorted by recency (most recent first).
Internal topic: t/72976.
This API allows plugins to transform a list of model objects before they're rendered in the UI. At the moment, this API is limited to items/lists of the experimental user menu, but it may be extended in the future to other parts of the app.
Additional context can be found in https://github.com/discourse/discourse/pull/18046.
Some of the changes in this PR are extracted from https://github.com/discourse/discourse/pull/17379.
Similar to the bookmarks tab in the new user menu, the messages tab also displays a mix of notifications and messages. When there are unread message notifications, the tab displays all of these notifications at the top and fills the remaining space in the menu with a list of the user's messages. The bubble/badge count on the messages tab indicates how many unread message notifications there are.
Some of the changes in this commit are extracted from https://github.com/discourse/discourse/pull/17379.
The bookmarks tab in the new user menu is different from the other tabs in that it can display a mixture of notifications and bookmarks. When there are unread bookmark reminder notifications, the tab displays all of these notifications at the top and fills the remaining space in the menu with the rest of the bookmarks. The bubble/badge count on the bookmarks tab indicates how many unread bookmark reminder notifications there are.
On the technical aspect, since this commit introduces a new `bookmark-item` component, we've done some refactoring so that all 3 "item" components (`notification-item`, `reviewable-item` and the new `bookmark-item`) inherit from a base component and get identical HTML structure so they all look consistent.
Internal tickets: t70584 and t65045.
