WebGLRenderer: Use Vogel disk sampling for PCF shadows

[mrdoob]

Description

This PR replaces the fixed grid PCF shadow sampling with Vogel disk sampling for improved shadow quality and performance.

Changes

• Implements Vogel disk sampling using the golden angle for evenly distributed sample points
• Adds interleaved gradient noise for per-pixel rotation to eliminate banding artifacts
• Reduces sample counts while maintaining/improving quality:
  • Directional/SpotLights: 17 → 12 samples (~29% faster)
  • Point lights: 9 → 8 samples (~11% faster)

Before (Shadow Radius: 1.0)	After (Shadow Radius: 1.0)

Before (Shadow Radius: 10.0)	After (Shadow Radius: 10.0)

This improvement probably makes SHADOWMAP_TYPE_PCF_SOFT redundant.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	355.14 86.33	355.6 86.58	+456 B +251 B
WebGPU	609.62 170.99	609.62 170.99	+0 B +0 B
WebGPU Nodes	608.23 170.72	608.23 170.72	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	486.77 121.07	487.22 121.32	+456 B +247 B
WebGPU	678.47 186.28	678.47 186.28	+0 B +0 B
WebGPU Nodes	620.47 169.54	620.47 169.54	+0 B +0 B