Neighbor list roadmap

[streeve]

Driven by discussion with about the HACCabana proxy app, we need new functionality for improved neighbor list performance:

LinkedCellList #712 (replaced #557)

• [x] NeighborList interface
• [x] new neighbor_parallel_for
• [x] new linkedcell_parallel

Add particle interaction functor overload to neighbor lists to compute directly rather than store neighbors:

• [ ] VerletList
• [ ] ArborX list

Add distributed neighbor search

• [ ] ArborX