docs: ES|QL Lens panels now support Discover drilldowns (#6352)

[florent-leborgne]

Summary

This PR addresses #6352 with the following changes:

• explore-analyze/dashboards/drilldowns.md — in the Create Discover drilldowns section, remove the outdated note that called out {{esql}} visualization panels as unsupported. Replace it with a bulleted list of supported panel types that mirrors the Create dashboard drilldowns list: **Lens visualizations that use a data view** (always) and **Lens visualizations built with {{esql}}** (tagged stack: ga 9.5 and serverless). The {{esql}} bullet carries a continuation paragraph (indented under the bullet, scoped by the bullet's tag) that describes the translation behavior: dashboard filters and the dashboard KQL or Lucene query are turned into a WHERE clause in the panel's ES|QL query; untranslatable filters are dropped; the Explore in Discover panel action applies the same translation. The cross-reference to Open panel data in Discover is preserved as a tip, framed as a no-drilldown alternative.
• explore-analyze/dashboards/drilldowns.md — in the existing Create dashboard drilldowns bullet list, reword the two Lens entries from **Visualizations created with Lens** / **{{esql}} visualizations** to **Lens visualizations that use a data view** / **Lens visualizations built with {{esql}}**. This removes the ambiguity that the first bullet could be read as covering all Lens visualizations (including ES|QL), and aligns the wording with the new Discover drilldowns list. Pre-existing applies_to tags on the ES|QL bullet (stack: ga 9.4, serverless) are preserved.
• explore-analyze/visualize/esorql.md — in the Add drilldowns to an {{esql}} visualization section, remove the now-stale note saying Discover drilldowns aren't available, and restructure the section as a bulleted list of the three supported drilldown types (Dashboard, URL, Discover). The new Discover bullet carries an inline {applies_to} tag for stack: ga 9.5 and serverless and briefly notes the filter/query translation behavior. The EVAL/STATS trigger constraint paragraph is preserved as a follow-on so it scopes all three bullets.

Discover drilldowns remain Lens-only at HEAD: the drilldown is registered solely in x-pack/platform/plugins/shared/lens/public/plugin.ts and gated to LENS_EMBEDDABLE_TYPE in its isCompatible check, so Maps, TSVB, Vega, aggregation-based, and Timelion panels are correctly absent from the new list.

Resolves

Closes #6352

Screenshots to add or update

• explore-analyze/dashboards/drilldowns.md — new {{esql}} content in the Create Discover drilldowns section: consider adding a screenshot of the resulting Discover view (translated WHERE clause visible in the ES|QL bar) since the prose describes runtime query rewriting that readers can't see in the existing data-view drilldown screenshot. The PR author's screenshots (1, 5) could be a starting point.

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🔍 Preview links for changed docs

• explore-analyze/dashboards/drilldowns.md
• explore-analyze/visualize/esorql.md

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[florent-leborgne]

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