[ES|QL] Support for First/Last - Unit Testing

[mouhc1ne]

Add ALL_FIRST/ALL_LAST unit tests, serialization tests, and documentation material (csv-test doc sample, md, json, etc.). The unit tests use the same logic as the existing FIST/LAST, which was refactored and moved to the abstract test class.

Here is what the two functions would look like if they were added to the docs.

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[github-actions]

🔍 Preview links for changed docs

• docs/reference/query-languages/esql/kibana/docs/functions/all_first.md
• docs/reference/query-languages/esql/kibana/docs/functions/all_last.md

[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

We use applies_to tags to mark version-specific features and changes.

Expand for a quick overview

When to use applies_to tags:

✅ At the page level to indicate which products/deployments the content applies to (mandatory)
✅ When features change state (e.g. preview, ga) in a specific version
✅ When availability differs across deployments and environments

What NOT to do:

❌ Don't remove or replace information that applies to an older version
❌ Don't add new information that applies to a specific version without an applies_to tag
❌ Don't forget that applies_to tags can be used at the page, section, and inline level

🤔 Need help?

• Check out the cumulative docs guidelines
• Reach out in the #docs Slack channel

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Pinging @elastic/core-docs (Team:Docs)

[craigtaverner]

LGTM

[craigtaverner]

At first I thought this was temporary, but see now it is shared between all four functions, so the removal of two functions still gives this class value.

[mouhc1ne]

Indeed. This one is definitely gonna survive the imminent blast heading straight to the existing first and last 🤣