[Metal-Epic:iOS] Directional Light graphics corruption when using the Metal Desktop Forward Renderer on iOS

When enabling the Metal Desktop Forward Renderer on iOS, Directional Light's with Light Shaft Bloom enabled will cause full screen graphics corruption when looking at the light source.

1. Create Blank Mobile Project with High Quality Setting, no Starter Content needed

1. Set Metal Shader Version to 1.2 and Enable Desktop Forward Renderer and disable Metal Mobile Renderer.

1. In the Directional Light, Enable Light Shaft Bloom

1. Oberserve pixelated, black/white screen whenever you look in the Light direction.