TSL: Rename premult to premultiplyAlpha

[sunag]

Description

Rename premult to premultiplyAlpha and update examples.

/cc @mrdoob @WestLangley

[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	554.99 153.64	554.99 153.61	-1 B -31 B
WebGPU Nodes	554.34 153.49	554.34 153.46	-1 B -31 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	629.96 170.36	630.02 170.38	+55 B +22 B
WebGPU Nodes	584.81 159.69	584.87 159.73	+55 B +38 B

[WestLangley]

@sunag Can you please check. This is breaking #31166 for me. That is, the line of code that multiplies by alpha is not being appended to the shader.

[sunag]

@sunag Can you please check. This is breaking #31166 for me. That is, the line of code that multiplies by alpha is not being appended to the shader.

Now it has been replaced by a function:

fn fn0 ( color : vec4<f32> ) -> vec4<f32> {

	return vec4<f32>( ( color.xyz * vec3<f32>( color.w ) ), color.w );

}
...
nodeVar = fn0( ... );