Introduce a checklist for visualizers, overrides etc

[teh-cmc]

Play with it live.

This adds a checklist that tries to cover as much as possible of the visualizer/overrides/defaults/etc stack with as little maintenance overhead as possible.

Once we're happy with it, we can derive it for different views/visualizers if there are specific things we want to check for.

This checks that adding and removing overrides & defaults work as expected for 2D views (both from the UI and from the SDK), and that they do the right thing rendering wise (using JPEGs as reference).

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 examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• 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
• Recent benchmark results
• Wasm size tracking

To run all checks from main, comment on the PR with @rerun-bot full-check.

[Wumpf]

<3

[teh-cmc]

Made a bunch of changes according to your feedback -- that's much better I think 👍

I'll wait for #6741 to be merged before finalizing this though, as this will change the expected results.

[Wumpf]

more clapping than before. Very good 😄