Part of https://projects.blender.org/blender/blender/pulls/141278
Blend files compatibility:
If a World exists and "Use Nodes" is disabled, we add new nodes to the
existing node tree (or create one if it doesn't) that emulates the
behavior of a world without a node tree. This ensures backward and
forward compatibility.
Python API compatibility:
- `world.use_nodes` was removed from Python API => **Breaking change**
- `world.color` is still being used by Workbench, so it stays there,
although it has no effect anymore when using Cycles or EEVEE.
Python API changes:
Creating a World using `bpy.data.worlds.new()` now creates a World with
an empty (embedded) node tree. This was necessary to enable Python
scripts to add nodes without having to create a node tree (which is
currently not possible, because World node trees are embedded).
Pull Request: https://projects.blender.org/blender/blender/pulls/142342
445eceb02a