NodeBuilder - Fix Interpolation

[cmhhelgeson]

Related Issue: #30576
Related PR: #30582

Description

As far as I'm aware, GLSL does not offer first and either forms of flat interpolation, so these shouldn't be mapped in GLSL.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	337.4 78.67	337.4 78.67	+0 B +0 B
WebGPU	553.93 153.5	553.89 153.48	-41 B -20 B
WebGPU Nodes	553.28 153.34	553.24 153.32	-41 B -19 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	468.59 113.33	468.59 113.33	+0 B +0 B
WebGPU	628.9 170.21	628.86 170.19	-41 B -22 B
WebGPU Nodes	583.76 159.55	583.72 159.53	-41 B -20 B