Fix Shadow compilation using shaderGraph (URP/HDRP) (#77)

* *Prepare a proper way to test different shadow cases

* prepare a shadow graph unlit (modifying alpha)

* Add reference data for shadow test

* Minimal data for reproduce issue 1259511

* Fix shadowpath using common integration of PassDepthOrMV & adding VFX_PASSDEPTH_SHADOW define

* *Update ShadowMaterial

* *Update ShaderGraphShadow.vfx

* *Move shader to common testing asset

* Add equivalent test for URP

* Add graphicTest for URP

* *Update reference images

* Fix display of alphaTreshold slider with shaderGraph : only if transparent using motionVector or shadowCasting

* Fix alphaClipping condition (will require validation of @shader-graph) : use proper boolean synchronized instead of testing slot presence

* Fix incorrect block listing

* *Update changelog.md

* Fix pass selection for lit effect

* Early remove ports which aren't active in VFXTarget : save code compilation & cleaner solution

* Voluntary add disabled branch on shadow unlit to cover alphaTreshold case

* *Minor comment

* Fix return alpha clipping (missing actual alpha test enabled)

* *Restore deleted file (to minimize change in MR, these files can be directly deleted on vfx/staging)

* VFX Graph Bugfix for shader compilation error in scene selection pass: 'Shaderpass should be defined at this stage.'

# Conflicts:
#	com.unity.visualeffectgraph/Shaders/ParticlePlanarPrimitives/PassDepthOrMV.template

* Revert unexpected change iVisualEffectGraph_HDRP\ProjectSettings\EditorBuildSettings.asset

* *Update reference image & Fix treshold for URP scene which was really too low (set to default 5e-4f)

* Fix issue https://github.cds.internal.unity3d.com/unity/vfx-graphics/pull/77#discussion_r69288

It was a bad merge

Co-authored-by: pastasfuture <pastasfuture@gmail.com>