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.

db/post_migrate/20220202201015_remove_trust_level_from_accounts.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class RemoveTrustLevelFromAccounts < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    safety_assured { remove_column :accounts, :trust_level, :integer }
+  end
+end