[Notifications] Add a Mentions tab (#7044)

* Split out NotificationsTab

* Remove unused route parameter

* Refine the split between components

* Hoist some logic out of NotificationFeed

* Remove unused option

* Add all|conversations to query, hardcode "all"

* Add a Conversations tab

* Rename to Mentions

* Bump packages

* Rename fields

* Fix oopsie

* Simplify header

* Track active tab

* Fix types

* Separate logic for tabs

* Better border for first unread

* Highlight unread for all only

* Fix spinner races

* Fix fetchPage races

* Fix bottom bar border being obscured by glimmer

* Remember last tab within the session

* One tab at a time

* Fix TS

* Handle all RQKEY usages

* Nit

src/lib/routes/types.ts

@@ -75,7 +75,7 @@ export type SearchTabNavigatorParams = CommonNavigatorParams & {
 }
 
 export type NotificationsTabNavigatorParams = CommonNavigatorParams & {
-  Notifications: {show?: 'all'}
+  Notifications: undefined
 }
 
 export type MyProfileTabNavigatorParams = CommonNavigatorParams & {
@@ -90,7 +90,7 @@ export type FlatNavigatorParams = CommonNavigatorParams & {
   Home: undefined
   Search: {q?: string}
   Feeds: undefined
-  Notifications: {show?: 'all'}
+  Notifications: undefined
   Hashtag: {tag: string; author?: string}
   Messages: {pushToConversation?: string; animation?: 'push' | 'pop'}
 }
@@ -102,7 +102,7 @@ export type AllNavigatorParams = CommonNavigatorParams & {
   Search: {q?: string}
   Feeds: undefined
   NotificationsTab: undefined
-  Notifications: {show?: 'all'}
+  Notifications: undefined
   MyProfileTab: undefined
   Hashtag: {tag: string; author?: string}
   MessagesTab: undefined