Shadow cascades can be cross-blended using dithering

[mvaligursky]

Feature

Directional light shadow cascades can be cross blended using dithering, instead of being a hard line switch. This looks relatively fine with textured objects, but it is an improvement even without it, where dithering is more obvious.

new public API:

LightComponent.cascadeBlend - value between 0 and 1, defaults to 0

without dithering:

with dithering:

In the future we can further improve this. When TAA is enabled, we can use moving blue noise to have per frame randomized dithering, which TAA would renoise. Added here

Fixes

Fixes to issues where additional / incorrect shaders were being compiled when changing light properties:

• internally shader generation options clone lights, and those lights were invalidating layers and generating new shaders. Now layer is invalidated only by a light assigned to it.
• normalOffsetBias has updating the key before modifying the value, so the keys were not correct, and would cause another shader generation of the next property update.