This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
In order to properly support the resource sharing paradigm, Occluders are split into Instances and Resources in the VisualServer. Instances are owned by a Scenario, and Resources are global. OccluderShape resources can now correctly be shared by multiple OccluderInstances.
Add framework for supporting geometrical occluders within rooms, and add support for sphere occluders.
Includes gizmos for editing.
They also work outside the portal system.
