Improvements:
* Occluder3D is now an abstract type inherited by: ArrayOccluder3D, QuadOccluder3D, BoxOccluder3D, SphereOccluder3D and PolygonOccluder3D. ArrayOccluder3D serves the same purpose as the old Occluder3D (triangle mesh occluder) while the rest are primitives that can be used to manually place simple occluders.
* Occluder baking can now apply simplification. The "bake_simplification_distance" property can be used to set a world-space distance as the desired maximum error, set to 0.1 by default.
* Occluders can now be generated on import. Using the "occ" and "occonly" keywords (similar to "col" and "colonly" for colliders) or by enabling on MeshInstance3Ds in the scene's import window.
Fixes:
* Fixed saving of occluder files after bake.
* Fixed a small error where occluders didn't correctly update in the rendering server.
Bonus content:
* Generalized "CollisionPolygon3DEditor" so it can also be used to edit Resources. Renamed it to "Polygon3DEditor" since it was already being used by other things, not just colliders.
* Fixed a small bug in "EditorPropertyArray" where a call to "remove" was left after the "remove_at" rename.
- Back to 1-based layer names to make it clearer in editor UI
- Layer bit accessors are renamed to layer value and 1-based too
- Uniform errors and documentation in render and physics
- Fix a few remaining collision_layer used in place of collision_mask
* Clean-up of node_3d_editor_plugin.{h,cpp}: removed unused code, fixed some bugs.
* Moved node_3d_editor_gizmos.{h,cpp} to editor/plugins.
* Added support for multiple gizmos per node. This means custom gizmos will no longer override the built-in ones and that multiple gizmos can be used in more complex nodes.
* Added support for handle IDs. When adding handles to a gizmo, an ID can be specified for each one, making it easier to work with gizmos that have a variable number of handles.
* Added support for subgizmos, selectable elements that can be transformed without needing a node of their own. By overriding _subgizmo_intersect_frustum() and/or _subgizmo_intersect_ray() gizmos can define which subgizmos should be selected on a region or click selection. Subgizmo transformations are applied using get/set/commit virtual methods, similar to how handles work.
Added an occlusion culling system with support for static occluder meshes.
It can be enabled via `Project Settings > Rendering > Occlusion Culling > Use Occlusion Culling`.
Occluders are defined via the new `Occluder3D` resource and instanced using the new
`OccluderInstance3D` node. The occluders can also be automatically baked from a
scene using the built-in editor plugin.
