Support for Unity URP SSAO

[anonymous2585]

Describe the problem

We use the MRTK shader for a multi platform project. We wanted to add an SSAO graphics option on powerfull platforms (PC), but the MRTK shader doesn't support it when set to "Depth Normal" mode, because some passes are missing in the shader. We were forced to use the "Depth" mode.

Describe the solution you'd like

Implementation of the Unity URP SSAO system in the shader.

Additional context

We added it locally and I will do a PR when I find the time.

Of course, don't activate URP SSAO on Hololens, it eats to much performances!

[Cameron-Micka]

Thanks for opening this issue!