Feature: partial/non closed meshes sim

[Dmeerev]

Core of feature is to add possibitity to make simulation on selected area of mesh: e.g half of cube is simulated (good if there will be checkmark to pin to other "static" part, or set it free of pinning, e.g. unconstrained by position), other stays still and can be animated, or two different sim's on two halves of cube, or one side is simulation, but other is collider.

[Vollkornaffe]

@Dmeerev would it be sufficient for your use case to have two separate objects instead?

I don't think it'll be much different once the input made it to the simulation engine, but it might not be easy to realize in UI otherwise.