[EEVEE] Expose Render Passes

There are a lot of requests for all sorts of trivial render features such as screenspace curvature, pixel depth offset and other things.

Most of these features users could probably create themselves if the different internal Render Passes were exposed to the user in nodes so users could create their own post-processing effects or more advanced materials.

For example:

The same way the "LightPath" node exposes information

A new node could be added called "RenderPasses"

Exposing these alone would already allow for much more advanced material creation.

But, when it comes to Screen Space Effects such as Bloom, DoF, and SSR some more would be required. As far as I know, these post-processing effects are usually done by drawing the final render pass into a render target texture. And then drawing a quad in front of the camera with a material applied to it that uses this Final Render Target with whatever effects you want to apply to it. Blender already does this with EEVEEs effects, but I am unsure what the easiest way would be for users to add their own.

Anyways, I think this would be a great feature that would get rid of a lot of suggestions at once without requiring devs to implement each render feature request one by one.