FIX: Make sure max_oneboxes_per_post is enforced (#16215)

PostAnalyzer and CookedPostProcessor both replace URLs with oneboxes.
PostAnalyzer did not use the max_oneboxes_per_post site and setting and
CookedPostProcessor replaced at most max_oneboxes_per_post URLs ignoring
the oneboxes that were replaced already by PostAnalyzer.

app/models/post_analyzer.rb

@@ -31,7 +31,11 @@ class PostAnalyzer
       cooked = PrettyText.cook(raw, opts)
     end
 
+    limit = SiteSetting.max_oneboxes_per_post
     result = Oneboxer.apply(cooked) do |url|
+      next if limit <= 0
+      limit -= 1
+
       @onebox_urls << url
       if opts[:invalidate_oneboxes]
         Oneboxer.invalidate(url)