Remove Axes3D archetype and add axis_length to Transform3D

[jleibs]

What

• Resolves: Transform3DArrows causes non-spatial archetypes to have applicable visualizers in 3d spaces #6578

It turns out having a visualizer with no required entities causes all kinds of problems. This moves us back to only allowing axes if you have a transform at an entity.

The heuristics are still a bit fancy for backwards compatibility. We don't use Transform3D as an indicator since that would cause every transform to get axes by default. Instead, we only create the Transform3D visualizer if:

• If we have no other visualizers, but otherwise meet the criteria for Transform3DArrows.
• If someone set an axis_length explicitly, so AxisLengthDetector is applicable.
• If we already have the CamerasVisualizer active.

Shortcomings

• The one big shortcoming still present here is that there's still no way to use a default to force the Transform3D axes to be visible.

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[github-actions]

Deployed docs

Commit	Link
1ea7320	https://landing-647srzau8-rerun.vercel.app/docs

[Wumpf]

good work! Still messy and we're surely not done here, but a good step forward

another thing for the shortcoming list: override of axislength will not make the arrows show up either