FEATURE: better UI to manage 2fa (#19338)

In this PR, we introduced an option, that when all authenticators are disabled, but backup codes still exists, user can authenticate with those backup codes. This was reverted as this is not expected behavior.

https://github.com/discourse/discourse/pull/18982

Instead, when the last authenticator is deleted, backup codes should be deleted as well. Because this disables 2fa, user is asked to confirm that action by typing text.

In addition, UI for 2fa preferences was refreshed.

spec/serializers/admin_user_list_serializer_spec.rb

@@ -31,18 +31,6 @@ RSpec.describe AdminUserListSerializer do
     end
   end
 
-  context "when backup codes enabled" do
-    before do
-      Fabricate(:user_second_factor_backup, user: user)
-    end
-
-    it "is true" do
-      json = serializer.as_json
-
-      expect(json[:second_factor_enabled]).to eq(true)
-    end
-  end
-
   describe "emails" do
     fab!(:admin) { Fabricate(:user, admin: true, email: "admin@email.com") }
     fab!(:moderator) { Fabricate(:user, moderator: true, email: "moderator@email.com") }

spec/serializers/current_user_serializer_spec.rb

@@ -102,16 +102,6 @@ RSpec.describe CurrentUserSerializer do
         expect(json[:second_factor_enabled]).to eq(true)
       end
     end
-
-    context "when backup codes enabled" do
-      before do
-        User.any_instance.stubs(:backup_codes_enabled?).returns(true)
-      end
-
-      it "is true" do
-        expect(json[:second_factor_enabled]).to eq(true)
-      end
-    end
   end
 
   describe "#groups" do

spec/serializers/user_serializer_spec.rb

@@ -250,16 +250,6 @@ RSpec.describe UserSerializer do
           expect(json[:second_factor_enabled]).to eq(true)
         end
       end
-
-      context "when backup codes enabled" do
-        before do
-          User.any_instance.stubs(:backup_codes_enabled?).returns(true)
-        end
-
-        it "is true" do
-          expect(json[:second_factor_enabled]).to eq(true)
-        end
-      end
     end
 
     describe "ignored and muted" do