Add the follow test scene for transparent depth pre & post pass

It should cover all material and master node types that support this feature.

Each "test" is setup in this way :

• Two meshes of overlaping quad, green is the tested material, red is a regular transparent
• One opaque object going through them
• The bottom quad is in the far depth of field blur zone, the middle one is in focus, and the top one is in the near blur zone
• The Pre & Post quad are cut diagonaly (like the blue opaque object) with prepass only on the top/left half and postpass on the rest

Yamato: (Select your branch):
https://yamato.prd.cds.internal.unity3d.com/jobs/902-Graphics/tree/HDRP%252Ftests%252Fpre-post-pass

Tests are running on yamato to generate reference images, don't merge yet.