This commit adds a tab for assignments in the experimental user menu. The assignments tab behaves very similarly to the bookmarks and messages tab in core: it displays the user's unread assign notifications first and then fills the rest of available space in the menu with assignments (same content that the current user menu displays).
More details of the experimental user menu can be found in https://github.com/discourse/discourse/pull/17379.
Krzysztof Kotlarek
Osama Sayegh