Add interactive explorers to an existing interactive editing session

[brollb]

It would be great to be able to load additional interactive explorers/editors in an existing interactive editing session. This would make it possible to create simple, composable interactive editors/explorers and load them into a single session. For example, this could enable the user to load an interactive training editor and then debug it (w/o leaving) by adding various dataset visualization utilities into the session to detect data issues.

One outstanding challenge is detecting unsaved artifacts for visualization.

[brollb]

This is the default behavior when creating multiple interactive editors but still needs some work to be possible for interactive explorers, too.