Port star material to BSL #552
Description
Star material is currently a ShaderMaterial. However it would be better to make it BSL based in order to make it more integrated with BabylonJS features and allow to generate WGSL instead of translating from GLSL at runtime.
For this, change StarMaterial class to hold a single material: NodeMaterial member, that can be accessed with a get() method and disposed using a dispose() method.
The constructor of the class builds the BSL shader, you can take inspiration from other BSL based shaders (look for "bsl" in the codebase).