perf: Improve `MaterialHelper` tree-shaking with `LightConstants`
perf: Improve `MaterialHelper` tree-shaking with `LightConstants`

`MaterialHelper` don't need the whole `Light` class (only the `Light` TypeScript type).

Related to https://github.com/BabylonJS/Babylon.js/issues/10388

RaananW/Babylon.js,sebavan/Babylon.js,RaananW/Babylon.js,sebavan/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,BabylonJS/Babylon.js