*Add callbacks to LWRP that can be attached to a camera. **IBeforeCameraRender **IAfterDepthPrePass **IAfterOpaquePass **IAfterOpaquePostProcess **IAfterSkyboxPass **IAfterTransparentPass **IAfterRender *Add test for callbacks *Clean up LWRP creation of render textures. If we are not going straight to screen ensure that we create both depth and color targets. https://katana.bf.unity3d.com/projects/com.unity.render-pipelines/builders?automation-tools_branch=add-platform-filter&ScriptableRenderLoop_branch=tim%2Flwrefactor&unity_branch=trunk