[Texturing] Allow to convert on the fly any depth-based layer into normalmap layer

[Vexod14]

Hello there =)

The goal is to allow a more precise retouching of said depth. When you pick a depth value, it's a "flat" value, which means you can only fix flat areas of depth, any gradient, bevels, chisels...etc can't be tweaked manually (well, you can, but with a huge lot of patience)

What I suggest is to allow user to paint on a normalmap version of the depth of any desired layer, meaning he won't be painting "colors" into the albedo channel, but on the normalmap channel. This would improve how far one could go about dealing with normalmap details, you could sculpt an entire wall with just painting colors.

A fantastic game artist, Romain Durand, already does that with photoshop and the results are stunning, fully artistically controlled. Here is one example of his work done this way : 

Latest wonderful point would be to keep depth consistent while modifying the normalmap, so you could switch back to the depth and use its, in fact, depth features. Each modes have different strength we could benefit from =)