Move distributed data structures and kernels to src/runtime/distributed/

[daphne-eu]

In GitLab by @pdamme on Jul 30, 2021, 18:59

The distributed data structures (Handle.h) and kernels (Distribute.h, DistributedCompute.h, and DistributedCollect.h) currently reside in src/runtime/local/. However, they clearly belong to the distributed run-time. Thus, the directories src/runtime/distributed/datastructures and src/runtime/distributed/kernels should be created and those files moved there.

This necessitates changes to genKernelInst.py and kernels.json, since these currently assume local kernels. We could add a boolean flag isDistributed to all kernels in kernels.json (or genKernelInst.py could just check if the kernel header resides in local or distributed).