- Use 3 bounces by default.
- Enable environment lighting from the scene by default.
- This is not done in `3.x` for compatibility with existing projects,
but it makes sense to do this by default since pretty much all
outdoor scenes benefit from this.
- Set the custom environment color to white (like ReflectionProbe).
- Its default energy is still 0, so it's invisible by default.
- Enable the generation of dynamic object probes by default.
- Tweak the `max_texture_size` property hint for better usability.
- Improve error messages when passing invalid sizes to
`LightmapGI.set_max_texture_size()`.
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