New compute at interface (#1743)

Rewrite of the compute at pass to rely on the new propagation mechanisms.

Author: zasdfgbnm

build_variables.bzl

@@ -642,6 +642,7 @@ libtorch_cuda_core_sources = [
     "torch/csrc/autograd/functions/comm.cpp",
     "torch/csrc/jit/codegen/cuda/arith.cpp",
     "torch/csrc/jit/codegen/cuda/compute_at.cpp",
+    "torch/csrc/jit/codegen/cuda/inline_propagator.cpp",
     "torch/csrc/jit/codegen/cuda/compute_at_map.cpp",
     "torch/csrc/jit/codegen/cuda/codegen.cpp",
     "torch/csrc/jit/codegen/cuda/contiguity.cpp",