[LuxCore + BlendLuxCore] [v2.11] Breaking Change - ShadowColor + Light Tracing Behavior

[CodeHD]

For the v2.11 release, I unified a different behavior between BiDir and Path+Light that will lead to scenes rendering different (for Path+Light) when:

• Shadow color is being used (i.e. it is not black)
• Light-tracing is used

The BiDir engine is unchanged as its implementation was the reference.

The original problem, leading to the implementation in BiDir, was described in this forums post (with example images):
viewtopic.php?f=4&t=4219

The contrasting observation for Path+Light (with example images) was posted in this GitHub issue:
https://github.com/LuxCoreRender/LuxCore/issues/671

Additional explanation:
The mechanism of shadow color is a biased technique, and using it leads to different behavior between path- and light-rays unless some explicit decision is made.
In case these paths are very similar, this just leads to double brightness. (See the linked original problem)
In case the paths are very different, there may be some merit for artistic applications. (See the linked GitHub Issue)

In addition to the unified behavior, BlendLuxCore now features an "override" setting that allows light-tracing rays when the shadow color is not black.