Maintain deep expanded state of inspector.

[mbostock]

From observablehq/notebook#201:

Inspector collapse/expand state is maintained on the top level, but not when those inspectors are nested. Ideally we can maintain as much expanded/collapsed state as possible: clearest way to do this would be to maintain a list of expanded keypaths, and expand them when there's new output.

[mbostock]

Here’s a good test case where this would be extremely useful:

https://selecttransform.github.io/site/

As it stands currently, it’s difficult to see the results of the transform interactively because every time you re-evaluate it collapses back to a single level.

I wonder if, related to this, we want a way to expand an entire level? Like option-click in the finder, but of course we don’t want to open every folder recursively forever, since that could hang. Maybe option-click would expand or collapse everything at the same level in the inspector?

[mbostock]

Moved to observablehq/inspector#12.