MicroSplat Mesh Module, vertex painting instead of texture based

The mesh module and MicroSplat use splat maps stored in textures. This new option allows you to use splat maps stored in the vertices of the mesh, which has many advantages and disadvantages discussed in the video, However, this opens the doors to easy workflows for voxels and other meshes where UV maps are problematic, and can give performance advantages in some use cases as well.