GLSLNodeBuilder: Fix texture() code generation for depth texture

[shotamatsuda]

Description

Following the discussion in #31760, this PR fixes an issue where texture() in WebGLBackend generating incorrect UV code, resulting a GLSL compilation error.

The argument to GLSL's texture() can be vec4, when the sampler is sampler2DArrayShadow for example, but the uvSnippet in generateTexture should not be assumed to be vec3, and it should be handled separately.
https://github.com/mrdoob/three.js/blob/r179/src/renderers/webgl-fallback/nodes/GLSLNodeBuilder.js#L403

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.91 79.11	338.91 79.11	+0 B +0 B
WebGPU	579.39 159.66	579.36 159.65	-32 B -11 B
WebGPU Nodes	578 159.42	577.97 159.4	-32 B -12 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	470.78 113.9	470.78 113.9	+0 B +0 B
WebGPU	649.54 175.53	649.51 175.52	-32 B -11 B
WebGPU Nodes	603.64 164.67	603.6 164.66	-32 B -10 B

[RenaudRohlinger]

Nice, we could simplify a bit like this:

generateTexture( texture, textureProperty, uvSnippet, depthSnippet, offsetSnippet ) {

	if ( depthSnippet ) uvSnippet = `vec3( ${ uvSnippet }, ${ depthSnippet } )`;

	if ( texture.isDepthTexture ) {

		if ( offsetSnippet ) return `textureOffset( ${ textureProperty }, ${ uvSnippet }, ${ offsetSnippet } ).x`;

		return `texture( ${ textureProperty }, ${ uvSnippet } ).x`;

	}

	if ( offsetSnippet ) return `textureOffset( ${ textureProperty }, ${ uvSnippet }, ${ offsetSnippet } )`;

	return `texture( ${ textureProperty }, ${ uvSnippet } )`;

}