Improved relax sculpt brush feature idea

I think what the relax brushes from sculpt mode are missing is a better volume preservation system

right now, it's preserving the current shape which, as we all have noticed, the vertices are loosing track of the original mesh volume as we keep sliding them around

so to fix it, there could be a little button in the brush settings which would create a duplicate of the mesh, and act as a shrinkwrap target

from there, we can freely slide the vertices around without loosing mesh volume progress

kinda like the "Set Persistent Base" option from the layered sculpt brush