LightShadow: Introduce biasNode.

[Mugen87]

Fixed #31191.

Description

Introduces LightShadow.biasNode as a node-based alternative to bias. When set, bias has no effect.

This gives the user more freedom in computing bias values e.g. based on the geometry data or distance values.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	356.54 84.66	356.54 84.66	+0 B +0 B
WebGPU	621.76 172.66	621.77 172.67	+12 B +8 B
WebGPU Nodes	620.36 172.43	620.37 172.43	+12 B +8 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	489.35 119.68	489.35 119.68	+0 B +0 B
WebGPU	692.73 187.97	692.78 187.99	+56 B +18 B
WebGPU Nodes	642.4 175.15	642.46 175.17	+56 B +19 B