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.

spec/controllers/api/v1/trends/tags_controller_spec.rb

@@ -7,10 +7,9 @@ RSpec.describe Api::V1::Trends::TagsController, type: :controller do
 
   describe 'GET #index' do
     before do
-      trending_tags = double()
-
-      allow(trending_tags).to receive(:get).and_return(Fabricate.times(10, :tag))
-      allow(Trends).to receive(:tags).and_return(trending_tags)
+      Fabricate.times(10, :tag).each do |tag|
+        10.times { |i| Trends.tags.add(tag, i) }
+      end
 
       get :index
     end