Nodes - Define Interpolation Type and Sampling Type of a VaryingNode

[cmhhelgeson]

Related issue: #30576

Description

Modifies VaryingNode, allowing the user to directly define interpolation and sampling types for a varying node. In cases where no interpolation is defined, the default optimizations/behavior stays in place.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.65 78.39	336.65 78.39	+0 B +0 B
WebGPU	522.23 144.94	523.1 145.15	+868 B +205 B
WebGPU Nodes	521.7 144.84	522.57 145.04	+868 B +205 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.64 112.24	465.64 112.24	+0 B +0 B
WebGPU	592.61 160.56	593.48 160.76	+868 B +202 B
WebGPU Nodes	547.74 150	548.61 150.21	+868 B +210 B

[cmhhelgeson]

I decided to just use @isaac-mason's basic sample for now, leaving the creation of a more dynamic sample for a later time. If possible, please include Isaac as a contributor to this PR.

[sunag]

It would be interesting to have the variables in the constants. For example: THREE.InterpolationType.PERSPECTIVE, THREE.InterpolationSampling.CENTROID...