Render pipeline currently in use.
This value is used to filter sub shaders based on the "RenderPipeline" tag. If a sub shader uses the "RenderPipeline" tag, it is used if and only if globalRenderPipeline matches the value completely. A sub shader that doesn't use the "RenderPipeline" tag will match all render pipelines. A matching sub shader is selected for all shaders when this value changes.