In particular:
* Remove all links (both asciidoc and markdown) from the JSON definition files.
* This required a two phase edit, from asciidoc links to markdown, and then removal of markdown (replace with markdown text). This is because the asciidoc does not have the display text, and because some links were already markdown.
* Split predicates into is_null and is_not_null
* We kept the old combined version because the main docs still use that, so now we have both combined and separate versions, and Kibana can select the version they want.
This PR was originally focused on improving support for Kibana docs, in particular the missing operator docs, but it has expanded to cover a bunch of related things:
* Primarily the main work was to improve operators support. ESQL generated docs cover all functions and most operators for which their is a clear operator class and test class. However, some are built-in behaviour and need additional support. This PR adds more generated content for those operators.
* Various specific operators requested by Kibana: Cast & null-predicates, and in particular the addition of examples
* Two functions without examples: mv_append and to_date_nanos
* Many small visual document cleanups (spelling, grammar, capitalization, etc.)
* Initial support for `applies_to` for multi-version differentiation.
This last point requires more work, as it is not yet agreed on just how we want this to look. We'll probably need to do refinements in followup PR. Consider the version in this PR as a first step into how this could look.
Did a few things:
* Rewrite Kibana docs asciidoc links to be MD links
* Make kibana docs links absolute to planned publication path
* Clarify which operators are generated and which are static
* Removed the trailing .md from kibana docs links
Earlier work on the ES|QL port of docs to V3 introduced an issue in the build.gradle file making it fail with --configuration-cache. This fixes that, as well as one other broken link and removes some unused files.
In addition we bring back partial support for deleting unused files. It is tricky to have full support for this due to the mix of static and generated content, particularly in the operators snippets.
In a few previous PR's we restructured the ES|QL docs to make it possible to generate them dynamically.
This PR just moves a few files around to make the query languages docs easier to work with, and a little more organized like the ES|QL docs.
A bit part of this was setting up redirects to the new locations, so other repo's could correctly link to the elasticsearch docs.
Building on the work started in https://github.com/elastic/elasticsearch/pull/123904, we now want to auto-generate most of the small subfiles from the ES|QL functions unit tests.
This work also investigates any remaining discrepancies between the original asciidoc version and the new markdown, and tries to minimize differences so the docs do not look too different.
The kibana json and markdown files are moved to a new location, and the operator docs are a little more generated than before (although still largely manual).
