[Xon] Search Improvements 2.17.2

A collection of improvements to XF's Enhanced Search and some for XenForo's default MySQL search.

MySQL & Elastic Search features;

• Allow * (or empty search string) to return results, for MySQL and XFES
• range_query search DSL
  • allows arbitrary range queries for numerical data
• Allow users to select the default search order independent for the forum wide setting.
  • Re-adds the global option for the default search type
• Display search terms on the search results page
• Add "Search only X" search criteria to individual handler pages, where X is thread/conversation/ticket/ect instead of searching thread/post etc.
  • Makes general search a true subset of member search

Elastic Search Only features:

• Add ability to push "can view threads/tickets by other" permission(s) into ElasticSearch query, reducing php-side culling of matching content.
  This improves searching forums/tickets where the user lacks these permissions.
  
  This is gated behind the option Push "View X by others" check into XFES', as it requires a full reindex. (Default disabled)
  
  Supports the following add-ons:
  • View Sticky Threads (free) add-on.
  • Collaborative Threads (paid) add-on.
  • @NixFifty's Tickets (paid) add-on.
  For best results, use ElasticSearch Essentials add-on, as it simplifies this permission constraint compared to stock XenForo
• Restore default search order option
• Per content type weighting
• Adds Elastic Search information to the AdminCP home screen.
• Adds a debug option to log the search DSL queries to error log for troubleshooting
• Option to extend search syntax to permit;
  • + signifies AND operation
  • | signifies OR operation
  • - negates a single token
  • " wraps a number of tokens to signify a phrase for searching
  • * at the end of a term signifies a prefix query
  • ( and ) signify precedence
  • ~N after a word signifies edit distance (fuzziness)
  • ~N after a phrase signifies slop amount
  • In order to search for any of these special characters, they will need to be escaped with \.
• "Specialized index" support
  • Specialized search index allows generating single-purpose elastic search indexes while re-using as much XF search infrastructure as possible.

  • Better tag autocomplete​

    Tag auto-complete powered by elasticsearch
    

    Better username autocomplete​

    Username auto-complete powered by elasticsearch
    These are examples of a "specialized index".
    
    The username autocomplete it creates an index with just the user/email and replaces the admin quick search and front-end username autocomplete with an elasticsearch powered version.
    
    The tag autocomplete replaces the front-end tag autocomplete with an elasticsearch powered version.
    
    In both cases this allows non-start-of-string matching, with typo tolerance.

Options: