Less restrictive visualizability constraints of 2D entities, improved space view generation heuristics

[Wumpf]

What

• Fixes Re-visit "child-of-root" space view spawning heuristics #4926
  • it does not address child-of-root heuristics for time series, but they weren't as much of a concern
• Fixes heuristic issues observed in Update to Rerun 0.13 cpp-example-opencv-eigen#20

Two changes in here:

• we no longer determine the dimensionality of a topological subspace, instead we only determine whether it can't display 2d/3d
  • 2d: we now state we can always display 2d objects
  • 3d: we can display it unless the parent of the active subspace is a pinhole in which case we only make the entity at the origin as visualizable
• make ViewCoordinates add "heuristic hints" to spatial topology
  • this is all that's needed to get rid of child-of-root heuristics in 3d without regressing existing examples

OpenCV example that didn't work before:

New release check:

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!

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[Wumpf]

converted to draft: just now tested all nightly examples on the web build and turns out that structure from motion creates an extra unwanted space view at camera

[Wumpf]

fixed, that was actually a pretty evil bug. Happy it didn't crash. added a test for it

[Wumpf]

from discussion with @jleibs on the phone:

• don't split via ViewCoordinates, this makes visualizability context a lot more complex
• instead note "interesting" roots within a SubSpace down (in SpatialTopology) so we can use this in the spawn heuristics
  • future work: we could so similar things for 2D?