Custom views must now provide reflection metadata

(This change only affects users of the Rust API for registering custom views.)

App::add_view_class now requires a ViewReflection argument describing which archetypes the view supports.

Before:

app.add_view_class::<MyView>()?;

After:

app.add_view_class::<MyView>(rerun::reflection::ViewReflection {
    applicability: rerun::reflection::ViewApplicability::Archetypes(vec![
        <rerun::archetypes::Points3D as rerun::Archetype>::name(),
    ]),
})?;

Use ViewApplicability::AllArchetypes for a custom view that is not dependent on any particular archetype.

This information may be used by the Viewer for various heuristics.