Native container component support

When writing game and engine code, we often find that we need to maintain and update a single long-lived datastructure, which may potentially be used by multiple systems. We've found it convenient in engine code to put such containers on Singleton components.

When a Native container is on a component, we enforce some restrictions on that component to ensure safety. In particular, we do not allow scheduling jobs against those components with IJobChunk or IJobEntity. This is because those jobs already access those components via containers, and the job safety system doesn't scan for nested containers, because that would make jobs take too long to schedule.

However, we do allow scheduling jobs against the containers themselves, so we get the component on the main thread, extract the container, and schedule the job against the container itself. The Singleton functions are specifically designed for this case and avoid completing unnecessary dependencies for this reason, so that you can chain jobs across multiple systems against the same container in a singleton component without creating a sync point.