Break out ES|QL functions/operators into single pages

[leemthompo]

Big sister issue of #2401

Complexity of fix

High, labor intensive. May need to be led by ESQL devs.

See elastic/elasticsearch#126279 for similar work.

What documentation pages are affected?

ESQL functions/operators syntax reference:

• Functions and operators:

Description

Users can't easily find documentation for specific ES|QL functions because they're all grouped on single, long pages:

• Aggregation functions
• Grouping functions
• Conditional functions and expressions
• Date-time functions
• IP functions
• Math functions
• Search functions
• Spatial functions
• String functions
• Type conversion functions
• Multivalue functions
• Operators

The content is difficult to scan and search.

Proposed solution

Split function documentation into individual pages:

• Create dedicated pages for each ES|QL function
• Create dedicated pages for each ES|QL operator
• Ensure all existing links redirect to the new individual pages

[craigtaverner]

My proposal for this would be:

• Changes to DocsV3Support (generated code)
  • Generate new per-function files in esql/functions-operators/functions/name.md that just includes esql/_snippets/functions/layout/name.md
  • Alternatively move the layout/name.md to be the new esql/functions-operators/functions/name.md with a smalll change to the file header
• Changes to static files
  • Change _snippets/lists/* to point to new files instead of tags
  • Change functions-operators/group.md files to only include lists, and not include layout files
  • Add all new function files in esql/functions-operators/functions/*.md to the toc.yml file
• Repeat the above for operators

[craigtaverner]

The above proposal does not deal with another aspect of this, which is right now we get a convenient On this page menu on the right, which for the functions is usually a list of the functions on that page. If we move to a function-per-page model, that list becomes meaningless. It would be replaced by an extra level in the left-side menu, so the capability will essentially move, but that does make the already complex, deeply nested menu even more complex and deeply nested.

[leemthompo]

It would be replaced by an extra level in the left-side menu, so the capability will essentially move, but that does make the already complex, deeply nested menu even more complex and deeply nested.

I'm not sure if it makes it more complex TBH or if it would be equivalent complexity just shifted around a bit. We'd just have to trade that off versus the big improvement this would unlock: better SEO and one-click to my function of interest from the SERP

But I agree that if we don't have unanimity on that last point, then it wouldn't be worth the effort.