Move geo-grid functions out of SNAPSHOT and into tech-preview

[craigtaverner]

The PR at #129581 added three new types: geohash, geotile and geohex, and support functions for creating these from strings, longs and geo_point fields. However all this was done under SNAPSHOT. Now it's time to move it into tech-preview.

[elasticsearchmachine]

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

[elasticsearchmachine]

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

[github-actions]

🔍 Preview links for changed docs

• docs/reference/query-languages/esql/functions-operators/spatial-functions.md
• docs/reference/query-languages/esql/functions-operators/type-conversion-functions.md
• docs/reference/query-languages/esql/kibana/docs/functions/st_geohash.md
• docs/reference/query-languages/esql/kibana/docs/functions/st_geohex.md
• docs/reference/query-languages/esql/kibana/docs/functions/st_geotile.md
• docs/reference/query-languages/esql/kibana/docs/functions/to_geohash.md
• docs/reference/query-languages/esql/kibana/docs/functions/to_geohex.md
• docs/reference/query-languages/esql/kibana/docs/functions/to_geotile.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

[alex-spies]

LGMT, thanks Craig! I like this. It's simple, contained, and can be easily reverted should we realize we need to for whatever reason. (Not that I know of any reason, of course!)

[alex-spies]

nit: javadoc is stale.

I like this. At first I thought we might as well remove this test, but asserting that the capability is enabled is actually better. Guards against accidentally disabling the capability and not noticing that we broke prod.

[craigtaverner]

Fixed the stale comment. I also think I might refine this test a little more when supporting geo_shapes, and it might increase more in value then.