GLSLNodeBuilder: Fix CubeDepthTexture sampler.

[Mugen87]

Related issue: #32801

Description

While trying to port the godrays effect from #32801 to TSL, I've realized a number of issues. One of them is fixed by this PR.

GLSLNodeBuilder currently assumes an instance of CubeDepthTexture is always sampled with samplerCubeShadow. However, this sampler type is only compatible when depth comparison is enabled. If you just want to access the raw depth (so when texture.compareFunction = null), you must use samplerCube.

Interestingly, WGSL allows to use texture_depth_cube() (and texture_depth_2d()) without the use of a comparison sampler. So a similar change isn't required for WebGPU.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	357.49 84.84	357.49 84.84	+0 B +0 B
WebGPU	622.01 172.8	622.06 172.81	+55 B +7 B
WebGPU Nodes	620.61 172.56	620.67 172.57	+55 B +8 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	490.47 119.9	490.47 119.9	+0 B +0 B
WebGPU	693.12 188.09	693.17 188.1	+55 B +13 B
WebGPU Nodes	642.5 175.19	642.56 175.2	+55 B +10 B