Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `app/models/account.rb`:
  Not a real conflict, just upstream getting rid of unused constants too close
  to glitch-soc-specific contents.
  Removed unused constants like upstream did.
- `app/models/trends.rb`:
  Conflict because glitch-soc disabled email notifications for trending links.
  Upstream has refactored this quite a bit and added trending posts.
  Took upstream code, but disabling the extra trending stuff will come in
  another commit.
- `app/views/admin/trends/links/index.html.haml`:
  Conflict due to glitch-soc's theming system.
  Ported upstream changes accordingly.

app/helpers/admin/filter_helper.rb

@@ -5,9 +5,10 @@ module Admin::FilterHelper
     AccountFilter::KEYS,
     CustomEmojiFilter::KEYS,
     ReportFilter::KEYS,
-    TagFilter::KEYS,
-    PreviewCardProviderFilter::KEYS,
-    PreviewCardFilter::KEYS,
+    Trends::TagFilter::KEYS,
+    Trends::PreviewCardProviderFilter::KEYS,
+    Trends::PreviewCardFilter::KEYS,
+    Trends::StatusFilter::KEYS,
     InstanceFilter::KEYS,
     InviteFilter::KEYS,
     RelationshipFilter::KEYS,