- Implement shadow fading when using the Orthogonal shadow mode
(like in `master`).
This allows customizing the distance at which directional shadows
start to fade away. Shadow fading will also always start at the same
distance now, regardless of the current shadow mode in use.
This is useful for enclosed levels to prevent shadows from fading
at all with a well-tuned maximum distance.
The default fade start value (0.8) results in fading happening later
in the distance compared to the previous behavior, where fading started
from the last shadow split distance (0.6 in PSSM 4 Splits and
0.1 in PSSM 2 Splits).
