xF2 Add-on Search Improvements 2.13.0

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

• Fix bug where 'weight by content type' feature didn't work as expected in general search
• Thanks to @NamePros for sponsoring this update.
• Display various search term constraints on the search results form.
  For developers to implement support in 3rd party add-ons:
  • Each search constraint needs a svSearchConstraint. prefixed phrase.
    Arrays are mapped to phrases by adding a _ for each sub-array/key as such; c[warning][points][lower] => svSearchConstraint.warning_points_lower
  • Each search order needs a svSearchOrder. prefixed phrase.
  • Extend XF\Entity\Search::getSpecializedSearchConstraintPhrase(string $key, $value) to provide custom phrase handling (ie node names)
  • Extend XF\Entity\Search::formatConstraintValue(string $key, $value) to provide custom formatting.
  • Extend XF\Entity\Search::setupConstraintFields to populate $svDateConstraint/$svUserConstraint/$svIgnoreConstraint properties which control formatting
• Use the debug option "List all unphrased search constraints" which will dump unmapped contraints to search results page.

• Fix incorrectly adding a return type to XF\Search\Search::isValidContentType
• Fix typo in admincp options phrase

• Fix "array_fill_keys() expects parameter 1 to be array, null given" error when content weighting has not been configured

This feature is powering tag autocomplete and username autocomplete which supports partial matches, and non-prefix lookups on SpaceBattles.

• Require XenForo 2.2+, removes xf2.0/xf2.1 support
• Add "Specialized index" support
  • Specialized search index allows generating single-purpose elastic search indexes while re-using as much XF search infrastructure as possible.
    • Elasticsearch index is more akin to an SQL table than an entire database, so for very specific tasks a single purpose search index works better.
    • A separate index also allows changing indexing properties and re-indexing just that one index without impacting the main search index
  • Implementation of a specialized index notes;
    At the core, a XenForo search handler is used to drive the functionality.
    • The search handler should implement the interface \SV\SearchImprovements\Search\Specialized\SpecializedData
    • Use the types MetadataStructure::KEYWORD or MetadataStructure::STR fields in setupMetadataStructure.
      These types will be rewritten to add .exact & [/icode].ngram[/icode] subfields. To skip this pass ['skip-rewrite' => true] to the MetadataStructure::addField's 3rd argument.
      • MetadataStructure::KEYWORD - shortish text which is semi-structured such as tags or usernames
      • MetadataStructure::STR - Arbitrary text which uses phrases of text
    • Register the search handler with the following content type fields
      • specialized_search_handler_class
      • entity
    • This handler really shouldn't be registered with search_handler_class content type field.
    • Add the behavior SV\SearchImprovements:SpecializedIndexable to the entity.

Example of the 'indexes page'

• Fix the "Default search order" option would get reset when changing "Search options" under Enhanced Search Setup page

• Improve extendibility of weight-by-content-type feature (Allow custom searches to opt-in to content weighting for single type searches)
• Improve compatibility with ElasticSearch v7+
• Support float-point weight values in weight by content-type
• Ensure XFES doesn't swallow the actual error message for a query failing instead of "all shards failed" message (backport for older versions of XFES)

• Improve extendibility of weight-by-content feature

• Allow weight-by-content to be extended.
• Compatibility update when resolving an extended class to the root class
• Require Standard Library by Xon v1.2.0+