Parent task to gather topics needed to get physics working in 2.8, mainly by updating physics systems to be copy-on-write aware.
* Hair Dynamics
* Dynamic Paint
This mainly involves sharing the point cache between the original and COW object. This was already done for rigid body, cloth and smoke, look at the relevant commits for examples of how to do it. Other issues:
* Dependency graph updates are not properly invalidating the point caches.
* With multiple view layers there should be different caches, or there should be some mechanism to resolve what happens when different objects are enabled on different view layers.