WebGPURenderer: Add cache for shadow nodes

[sunag]

Fixes #31872

Description

Add a cache to reuse the shadow nodes created from the material and update it if the material version is updated.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.24 79.14	338.24 79.14	+0 B +0 B
WebGPU	580.38 160.31	580.88 160.44	+491 B +125 B
WebGPU Nodes	578.99 160.07	579.48 160.19	+491 B +126 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	469.7 113.74	469.7 113.74	+0 B +0 B
WebGPU	649.92 175.87	650.41 175.98	+491 B +108 B
WebGPU Nodes	604.03 165.03	604.52 165.16	+491 B +121 B