Blender Git Loki

Fix #30004: cycles brightness/contrast node issues. The formula used did not work
very well for colors that can be outside of the 0.0..1.0 range, giving +/- infinity
results.

Now we just use a simple linear contrast factor as proposed by Paolo Sourvinos, and
clamp values to be >= 0, and also make the parameters work more in the 0..1 range
instead of the 0..100 range, to be more consistent with other nodes.