C++ columns method for convenient send_columns call through archetypes

[Wumpf]

Related

• Part of Tagged columnar updates: C++ #8754

What

C++ point send_columns example is now a lot shorter:

    // Partition our data as expected across the 5 timesteps.
    auto position =
        rerun::Points3D::update_fields().with_positions(positions).columns({2, 4, 4, 3, 4});
    auto color_and_radius =
        rerun::Points3D::update_fields().with_colors(colors).with_radii(radii).columns();

    rec.send_columns2("points", time_column, position, color_and_radius);

Left todo among other things:

• update all other examples
  • we'll likely need the with_many calls we introduced in Rust as well
• send_columns2 should become send_columns
  • this will be a breaking change -> add migration guide

[github-actions]

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| Result | Commit | Link | Manifest |
| ------ | ------- | ----- |
| ❌ | | https://rerun.io/viewer/pr/8828 | +nightly +main |

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