Add-ons Search Improvements 2.13.1

Thanks @NamePros for sponsoring this update

• Fix cached search results would be unexpectedly be viewable to anyone if they guessed the search result URL.
  • Affected versions; v2.8.1
  • These search URLs expire after a day
• Fix search term on search result pages leaking information for non-viewable content
  • Affected version; v2.7.4, v2.7.5 and v2.8.1
  • Fix leaking thread title when using "In thread" search area, and rendering a bad phrase if the thread doesn't exist
  • Fix linking to non-active user profiles when searching by members
• Workaround for an XF bug where the cached search results for a member search could be directly shared with a guest
  • Non-visible items on the result page where not rendered, but this does leak that there are hits in not viewable to guests areas.

Thanks @NamePros for sponsoring this update

• Fix "before" search result term would print an integer instead of a human readable yyyy-mm-dd formatted string
• Change 'no results found' handling to display search terms on the relevent page
  • If using ElasticSearch Essentials, recommend updating to v3.13.0+ as this change may impact some options which display on no results found.
• Fixes for search term on results page
  • Add missing "With X thread" search term
  • Fix "Users" search term could fail to render the list of usernames
  • Add the 'content type' search term

• Remove usage of utf8_* function(s), and use native php multi-byte functions instead.
• Fix HTML markup error in svPushViewOtherCheckIntoXFES option description