WebGPURenderer: Added geometry in material cache key

[sunag]

Description

This fixes some occasions where geometry is shared with different indexes.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	686.07 169.79	686.07 169.79	+0 B +0 B
WebGPU	832.67 223.1	832.7 223.11	+23 B +8 B
WebGPU Nodes	832.18 222.98	832.21 222.99	+23 B +8 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	462.42 111.53	462.42 111.53	+0 B +0 B
WebGPU	530.14 142.82	530.17 142.83	+23 B +8 B
WebGPU Nodes	486.8 132.68	486.82 132.69	+23 B +6 B

[aardgoose]

@sunag On my laptop this takes the webgpu_performance example from < 2s to display to around 13s.