FIX: Push category hashtag slug match to top (#19174)

When searching for categories it is possible for
a child category to have a slug that matches the term
exactly, but will not be found by .lookup since we
don't return these categories unless the ref matches
parent:child.

Introduces a search_sort method to each hashtag data
source so they can provide their custom sort logic of
results, in category's case putting all matching slugs
to the top regardless of parent/child relationship
then sorting by text.

plugins/chat/lib/chat_channel_hashtag_data_source.rb

@@ -40,4 +40,8 @@ class Chat::ChatChannelHashtagDataSource
       []
     end
   end
+
+  def self.search_sort(search_results, _)
+    search_results.sort_by { |result| result.text.downcase }
+  end
 end