New SG integration fallback to black on HDRP

Step to repro:

• Open a HDRP project
• Create a shader graph unlit
• Enable "Support VFX" in master node inspector
• Set the base color to red
• Save
• Create a default VFX
• Assign the newly created shaderGraph
• Spawn the newly created VFX in the scene
• Observe the expected red output
• Add an exposed keyword in shaderGraph
• Save the shaderGraph
• Observe the log : "keyword blackboard properties in Shader Graph are currently not supported in Visual Effect shaders. Falling back to default generation path"
• Observe in scene : the rendered particles are now black

Expected:

• The VFX should simply fallback ignoring the unsupported keyword

Bonus:

• The log warning isn't user friendly, usage of the VFX error feedback could be appropriate here.
• The same repro in URP generates compilation error