Removes some unnecessary includes from `editor_node.h`, and instead add
those where they're used.
Removes unnecessary `editor_node.h` includes in various editor classes.
Renames `dynamicfont` to `dynamic_font` in a couple files.
Misc cleanup while jumping through that rabbit hole.
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.
