Fix CSV-escaped quotes in generated docs examples

[quackaplop]

Summary

• DocsV3Support.renderTableLine() reads CSV spec result blocks as raw text but didn't unescape RFC 4180 quoting — quoted fields with doubled quotes ("") were rendered literally in Markdown tables
• Added CSV unescaping: strip outer " delimiters and replace "" with " so JSON strings render correctly in published docs
• Example: {"severity":"ERROR"} instead of {""severity"":""ERROR""}

Fixes these published doc pages

• JSON_EXTRACT — 5 example result tables show CSV-escaped JSON instead of proper JSON
• TO_TDIGEST — 1 example result table shows CSV-escaped JSON instead of proper JSON

Affected docs

• json_extract.md — 5 result cells with JSON values now render correctly
• to_tdigest.md — 1 result cell with JSON value now renders correctly

Test plan

• Precommit passes (spotless, checkstyle, forbidden APIs)
• JsonExtractTests — doc generation + function logic
• ToTDigestTests — doc generation + function logic
• CsvTests with *json* filter — CSV spec end-to-end
• Verified to_boolean.md NOT affected (empty string "" is preserved because the cell doesn't start/end with " as delimiters)

[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)

[leemthompo]

Docs output LGTM, but I'm not competent to validate the java changes :)