[WIP] [Model] Add "load model from code" feature

[w0wca7a]

PR Details

Enables loading 3D models (FBX, GLTF, OBJ, etc.) at runtime directly from code using MeshConverter, without requiring asset compilation or ContentManager.

Usage example:

using Stride.Core.Mathematics;
using Stride.Engine;
using Stride.Importer.ThreeD;

public class FileImporter : StartupScript
{
    public override void Start()
    {
        base.Start();
        if (Entity.Scene == null) return;

        string InputFile = "D:\\model.fbx";
        var model = ModelBuilder.CreateFromFile(GraphicsDevice, InputFile);
        var modelComponent = new ModelComponent(model);
        var importedEntity = new Entity("Imported", position: new Vector3(0, 1, 0)) { modelComponent };
        Entity.Scene.Entities.Add(importedEntity);
    }
}

Related Issue

N/A

Importan NOTE

At this time model can not be unload and load again #2101
Post-effects in graphics compositor also not working now and causes exceptions.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.