WGSLNodeBuilder: Fix use of sampler for vertex stage

[sunag]

Description

Use textureSampleLevel() for sampler-compatible textures and keep tsl_biquadraticTexture() for non-natively compatible textures.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.29 78.32	336.29 78.32	+0 B +0 B
WebGPU	548.37 152.03	548.2 152.02	-167 B -18 B
WebGPU Nodes	547.72 151.88	547.55 151.86	-167 B -18 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	466.23 112.58	466.23 112.58	+0 B +0 B
WebGPU	623.15 168.73	622.98 168.71	-167 B -21 B
WebGPU Nodes	578.02 158.02	577.85 158	-167 B -22 B