Merge commit 'b1a584d252f4df4c2a1a9400d6588b4f36768216' into glitch-soc/merge-4.3

Conflicts:
- `app/lib/feed_manager.rb`:
  Not a real conflict, but glitch-soc has an extra `populate_direct_feed` method.
  Added upstream's code.
  In addition, upstream changed how notifications from follow subscriptions were
  handled, refactoring this file in the process.
  Ported upstream's changes.
- `app/services/precompute_feed_service.rb`:
  Not a real conflict, glitch-soc has extra code for the direct feed.
  Added upstream's new code for populating lists.
- `app/validators/poll_options_validator.rb`:
  Upstream split `PollValidator` in two, and glitch-soc had local changes to
  make the options configurable.
  Refactored as upstream did, keeping glitch-soc's configurable limits.
- `app/workers/feed_insert_worker.rb`:
  Upstream changed how notifications from follow subscriptions were handled,
  refactoring this file in the process.
  Conflict is due to glitch-soc having an extra timeline type (direct).
  Ported upstream's changes.

app/controllers/api/v2/notifications_controller.rb

@@ -46,7 +46,7 @@ class Api::V2::NotificationsController < Api::BaseController
   end
 
   def show
-    @notification = current_account.notifications.without_suspended.find_by!(group_key: params[:group_key])
+    @notification = current_account.notifications.without_suspended.by_group_key(params[:group_key]).take!
     presenter = GroupedNotificationsPresenter.new(NotificationGroup.from_notifications([@notification]))
     render json: presenter, serializer: REST::DedupNotificationGroupSerializer
   end
@@ -57,7 +57,7 @@ class Api::V2::NotificationsController < Api::BaseController
   end
 
   def dismiss
-    current_account.notifications.where(group_key: params[:group_key]).destroy_all
+    current_account.notifications.by_group_key(params[:group_key]).destroy_all
     render_empty
   end