DEV: Add "delete user" options to illegal flag review (#29956)

We already add the "delete user" and "delete and block user" options to the drop-down for potential spam, but we should do this for potentially illegal posts as well.

This is entirely based on the implementation for the potential spam one, including caching the status on the reviewable record.

Also note that just as for potential spam, the user must be "deletable" for the option to appear.

I also took the liberty to move the options in the drop-down to what I think is a more intuitive place. (Between delete post and suspend/silence user.)

spec/models/reviewable_flagged_post_spec.rb

@@ -16,6 +16,13 @@ RSpec.describe ReviewableFlaggedPost, type: :model do
     expect(reviewable.reload.potential_spam?).to eq(true)
   end
 
+  it "sets `potentially_illegal` when an illegal flag is added" do
+    reviewable = PostActionCreator.off_topic(user, post).reviewable
+    expect(reviewable.potentially_illegal?).to eq(false)
+    PostActionCreator.illegal(Fabricate(:user, refresh_auto_groups: true), post)
+    expect(reviewable.reload.potentially_illegal?).to eq(true)
+  end
+
   describe "actions" do
     let!(:result) { PostActionCreator.spam(user, post) }
     let(:reviewable) { result.reviewable }
@@ -95,7 +102,26 @@ RSpec.describe ReviewableFlaggedPost, type: :model do
       end
 
       context "when flagged as potential_spam" do
-        before { reviewable.update!(potential_spam: true) }
+        before { reviewable.update!(potential_spam: true, potentially_illegal: false) }
+
+        it "excludes delete action if the reviewer cannot delete the user" do
+          post.user.user_stat.update!(
+            first_post_created_at: 1.year.ago,
+            post_count: User::MAX_STAFF_DELETE_POST_COUNT + 1,
+          )
+
+          expect(reviewable.actions_for(guardian).has?(:delete_user)).to be false
+          expect(reviewable.actions_for(guardian).has?(:delete_user_block)).to be false
+        end
+
+        it "includes delete actions if the reviewer can delete the user" do
+          expect(reviewable.actions_for(guardian).has?(:delete_user)).to be true
+          expect(reviewable.actions_for(guardian).has?(:delete_user_block)).to be true
+        end
+      end
+
+      context "when flagged as illegal" do
+        before { reviewable.update(potential_spam: false, potentially_illegal: true) }
 
         it "excludes delete action if the reviewer cannot delete the user" do
           post.user.user_stat.update!(