Add cell-based markdown editor for pages

[guerler]

Requires #19721. Extracted from #19226. This PR introduces a cell-based markdown editor as an alternative to the text-based editor for pages. The cell-based editor provides live previews but does not yet support inserting visualizations—this feature will be added in a separate PR. Users can seamlessly switch between the two editors. This change only impacts Pages, there are no changes to Reports at this time. There are some improvements and adjustments to this addition in the follow-up PR.

Screen.Recording.2025-03-15.at.10.11.32.AM.mov

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• This is a refactoring of components with existing test coverage.
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License

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[jmchilton]

Very cool new functionality to be sure and I'm excited to see visualizations hooked into these. My wish list is UI for existing directive parameters beyond "which dataset/collection/etc...", getting monaco instead of ACE into the app, handling directives outside formal blocks (#19086 / #8516). My anxiety is this doesn't head in those directions but I understand we have different wish lists.

[guerler]

Thank you! I appreciate your feedback.

Regarding visualizations, our wish lists might align in some areas but differ slightly—I do think we need long-term supported, PDF-exportable visualizations, as well as support for more complex interactive ones like Vitessce. Particularly now that we have a solid visualization framework.

I’ll be switching from Ace to Monaco once #19434 is merged. Once we make the switch, we could also leverage autocomplete to assist in writing reports, potentially allowing for a purely text-based process with only the code editor visible.

I'll also take a look at the referenced PRs. Thanks again!