Different icon for empty entity paths

[abey79]

What

This PR adds a subtly different icon for "empty" entities. By "empty", I mean "no component logged on the current timeline". This means that changing timeline may potentially change the icon of some entity (though it takes a somewhat contrived example to do so).

TODO:

•  do the same in blueprint tree after Remove groups from blueprints panel #5326 is merged

Fixes #5302

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
• If applicable, add a new check to the release checklist!

• PR Build Summary
• Docs preview
• Examples preview
• Recent benchmark results
• Wasm size tracking

[nikolausWest]

These look a little strange, otherwise great!

[abey79]

@nikolausWest good spot! These are an oversight from my previous PR. Will fix asap.

edit: #5341

[teh-cmc]

There is an inconsistency here: the data UI uses DataStore::all_components which is timeful, while this uses the EntityTree which is timeless.

I.e. scrubbing the time cursor might change the icon that appears in the blueprint panel and elsewhere, while that won't happen in the time panel.

I think that's fine (unless we want both to be timeless), but deserves a comment to specify that this was intentional at least.

[abey79]

As discussed, both were actually timeless, but instance_path_icon() accepting a Query argument was very confusing. I changed it to accept a Timeline instead, which is all it needs.

Also, I made both the streams and the blueprint have their icons based on the current timeline (in my original commit, the streams icon was based on all timeline).

[emilk]

nice!