Add GsplatMesh script and example for converting meshes to gaussian splats

[mvaligursky]

Summary

• Adds new GsplatMesh script (scripts/esm/gsplat/gsplat-mesh.mjs) that converts mesh geometry into gaussian splats
• Adds new example procedural-mesh.example.mjs demonstrating terrain and animated cloud conversion to splats

Details

GsplatMesh Script

A new script that extracts triangles from render components and generates uniformly distributed splats across mesh surfaces using scanline rasterization.

API:

const gsplatMesh = entity.script.create(GsplatMesh);
gsplatMesh.buildFromEntity(sourceEntity, {
    splatSize: 0.01,    // Size of each splat (default: 0.01)
    recursive: true,    // Search children for render components (default: true)
    margin: 0.65        // Edge margin relative to splatSize (default: 0.65)
});

Features:

• Extracts color from StandardMaterial (emissive if non-black, else diffuse)
• Supports transparent materials (uses material.transparent to detect)
• Splats are generated in local space relative to the source entity root
• Configurable margin to avoid overlap artifacts at shared triangle edges

Procedural Mesh Example

Demonstrates converting the terrain.glb scene to gaussian splats:

• Converts static terrain geometry to splats
• Converts cloud meshes to separate splat entities with transparency
• Clones and animates cloud splats in circular paths (matching shadow-cascades example)
• Includes reveal shader effect