TSL: Introduce struct

[sunag]

Related issue: #29908, #29760

Description

PR introduces struct for TSL following the styntax below:

const BoundingBox = struct( {
	min: 'vec3',
	max: 'vec3'
} );

// style 1
const bb = BoundingBox( vec3( 0 ), vec3( 1 ) );

// style 1 - default value
const bb = BoundingBox();

// style 2
const bb = BoundingBox( {
	min: vec3( 0 ), 
	max: vec3( 1 ) 
} );

// style 2 - optional values
const bb = BoundingBox( {
	// min: vec3( 0 ),  // use optional value
	max: vec3( 1 ) 
} );

// assigns in TSL Fn
const bbFn = Fn( () => {

	const bb = BoundingBox();

	const bbMax = bb.get( 'max' );
	bbMax.assign( vec3( 1 ) );
	// or -> bb.get( 'max' ).assign( vec3( 1 ) );

	return bb;

} );

// debug
material.colorNode = bbFn().get( 'max' );

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.27 78.29	336.27 78.29	+0 B +0 B
WebGPU	512.43 142.35	514.55 142.95	+2.11 kB +595 B
WebGPU Nodes	511.9 142.25	514.01 142.84	+2.11 kB +594 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.25 112.13	465.25 112.13	+0 B +0 B
WebGPU	586.38 159.04	587.2 159.31	+816 B +278 B
WebGPU Nodes	541.76 148.6	542.58 148.87	+816 B +268 B