[Xon] Search Improvements 2.15.9

• Update installer to verify ElasticSearch index does not require rebuilding when this add-on is installed/updated/rebuilt
• Return 400 status code instead of 200 when the search query is wrong

Compatibility fix for Username auto-complete using XFES and Tag auto-complete using XFES add-ons

Fix min/max range searches (ie word-count) where flipped when using MySQL full-text search

Fix guest user searches could be sent into a redirect loop depending on search criteria

Fix XF2.3.0 infinite search redirect for guests

Restore XF2.1 support
XF2.3 support
Fix "[E_DEPRECATED] Use of "parent" in callables is deprecated" on search

[*]Add "Push thread prefix text into search" option (default true)
[*]Supports ElasticSearch Essential's autocomplete
[*]Requires manual rebuild of threads on changing this option

Fix guests searching by user would restart the search query the first time they tried to visit the a different page of the search results

Requires StandardLib v1.19.0+
If installed, requires Redis Cache 2.17.0+
XF2.3 compatibility update
php 8.4 compatibility fix

• Require StandardLib v1.19.0+
• Code cleanup
• Add getSearchIdFromEntityId() helper method for transforming an XF entity id into the Elasticsearch index id