What

As the title says ☝🏻. Note that the icon still reflects visibility.

Here, the tab widget is visible but not the vertical one:

Selection panel (which currently doesn't reflect visibility state #4854):

Relates to:

• Make blueprint tree more scannable, and the concepts clearer by distinguishing containers, space views, and entities. #4743

Note: this PR piles on debt to be paid off with:

• Remove all formatting API from ListItem and use WidgetText's API instead #4802

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

• [PR Build Summary](https://build.rerun.io/pr/{{ pr.number }})
• [Docs preview](https://rerun.io/preview/{{ pr.commit }}/docs)
• [Examples preview](https://rerun.io/preview/{{ pr.commit }}/examples)
• Recent benchmark results
• Wasm size tracking