TSL Transpiler: Support struct definitions and declarations

[Ne0nWinds]

Related issue: #30885

Description

This PR adds support for struct definitions/declarations to the TSL transpiler.

Examples

Struct definitions:

struct Ray {
  vec3 origin;
  vec3 direction;
};

const Ray = struct({

	origin: 'vec3',
	direction: 'vec3'

}, 'Ray' );

Struct Declarations:

Ray r = Ray(vec3(0.0), vec3(0.0, 0.0, 1.0));

const r = Ray( vec3( 0.0 ), vec3( 0.0, 0.0, 1.0 ) );

Return Values / Input parameters:

// struct RaymarchResult { ... }

RaymarchResult raymarch(Ray r) {
	return RaymarchResult(vec3(0.0), 1.0);
}

export const raymarch = /*@__PURE__*/ Fn( ( [ r ] ) => {

	return RaymarchResult( vec3( 0.0 ), 1.0 );

}, { r: 'Ray', return: 'RaymarchResult' } );

Limitations

1. Struct members can't be properly accessed. Currently, if a struct member is accessed, the transpiler will generate .member instead of .get("member"). In order to do this properly, the transpiler would need proper type resolution. Some type information is available in the linker, but this won't work in the general case.

2. As far as I can tell (and I'm okay being corrected on this), TSL doesn't support structs with array/struct members, so this PR doesn't add support for them.

Despite these limitations, this feature still helps with the discoverability of struct syntax in TSL