[Q2 FY27] Unified visualization editor interface

Over the next months, the Lens UI is going to see major evolutions that will greatly impact the Lens documentation:

- Conversion to ES|QL/query mode
- Full flyout-based experience (with both regular and expanded flyout modes)
- "Lens" as a term is set to disappear to focus the experience on the outcome (build charts) rather than the editor (add Lens panels)

These product changes call for a deeper rework of the Lens docs, that will include:
- Chart-based documentation (that is already in progress through #1699)
- Integrating ES|QL/query mode experience to that chart-based documentation
- Revamp Lens docs with a new structure to better represent learning paths with tutorials, common tasks with well-scoped how-tos, and better links with apps where the flyout experience will be available (Not only dashboards but also Discover, etc.
- Look for current references to Lens and update that to match the new product approach
- Check how the structure around Lens docs might also need to evolve (other content panels, other "editors" such as Maps, Canvas, etc.)

\* The timeline of some of these items needs to be confirmed

Related epics:
https://github.com/elastic/kibana-team/issues/1753
https://github.com/elastic/kibana-team/issues/2160
https://github.com/elastic/kibana-team/issues/2159