Tagged components milestone 2: no more indicators

[teh-cmc]

The second milestone for tagged components is to remove the concept of indicator components entirely.
The semantics of the viewer must not be impacted in any way by that change.

• Remove all codegen related to indicator components.
• Replace all logic that relies on querying for indicators with new descriptor-based logic ("is there anything on that path that belongs to the Points3D archetype?").

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• Part of Tagged components #6889
• Requires Tagged components milestone 1: end-to-end tagging #7948

[teh-cmc]

Talked with @nikolausWest about the upgrade path and backwards compat.

We will need to:

• Slap a deprecated flag on all indicator types, but keep them around for the SDKs.
• Make sure that indicator types set the archetype_name in their descriptors, so the backend can find them by tag, without being aware of indicators at all.
• Make the backend entirely tag-driven.

That way that kind of user code still works:

rr.log("points", rr.ColorBatch(colors), rr.Points3D.indicator())

and because indicator types are deprecated, the user gets a warning along these lines:

WARN: Indicator components are deprecated, use `rr.log("points", rr.ColorBatch(colors).with_descriptor(archetype_name="Points3D"))` instead

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In the future, the SDK APIs will need to be much better to accommodate for custom tags and all, but that's another topic...