Use Mention arel/exist in report service scope build-out (#38300)

app/services/report_service.rb

@@ -88,11 +88,18 @@ class ReportService < BaseService
     has_followers = @target_account.followers.with_domain(domain).exists?
     visibility = has_followers ? %i(public unlisted private) : %i(public unlisted)
     scope = @target_account.statuses.with_discarded
-    scope.merge!(scope.where(visibility: visibility).or(scope.where('EXISTS (SELECT 1 FROM mentions m JOIN accounts a ON m.account_id = a.id WHERE lower(a.domain) = ?)', domain)))
+    scope.merge!(scope.where(visibility: visibility).or(scope.where(domain_mentions(domain))))
     # Allow missing posts to not drop reports that include e.g. a deleted post
     scope.where(id: Array(@status_ids)).pluck(:id)
   end
 
+  def domain_mentions(domain)
+    Mention
+      .joins(:account)
+      .where(Account.arel_table[:domain].lower.eq domain)
+      .select(1).arel.exists
+  end
+
   def reported_collection_ids
     @target_account.collections.find(Array(@collection_ids)).pluck(:id)
   end