Add support for custom picking data

[m-edlund]

Objective

• Adds the ability for picking backends to add custom hit data
• Fixes Extend the information included in HitData #16186

Solution

• Adds an extra field to the HitData struct which can take any Data that implements HitDataExtra. This is stored in an Arc which can be downcast with a helper function in the system that consumes the hit.
• In the original ticket I suggested using a generic, however this caused extensive code changes and complications down the line with the HoverMap and OverMap so I decided against it.

Testing

• I added an example custom_hit_data to test the new feature
• I tested all other picking examples to ensure they still work as expected
• I tested the examples on Ubuntu
• I additionally tested the custom_hit_data example in wasm

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Showcase

Click to view showcase

Creating custom hits:

let picks: Vec<(Entity, HitData)> = ray_cast
            .cast_ray(ray, &settings)
            .iter()
            .map(|(entity, hit)| {
                let extra = TriangleHitInfo {
                    triangle_vertices: hit.triangle,
                };

                let hit_data = HitData::new_with_extra(
                    ray_id.camera,
                    hit.distance,
                    Some(hit.point),
                    Some(hit.normal),
                    extra,
                );

                (*entity, hit_data)
            })
            .collect();

Reading custom hits:

   for hits in pointer_hits.read() {
        for (_, hit) in &hits.picks {
            let Some(info) = hit.extra_as::<TriangleHitInfo>() else {
                continue;
            };
            let Some(vertices) = info.triangle_vertices else {
                continue;
            };

            // do something cool with your custom hit data
        }
    }

An example of what you can do with this