[TensorExpr] Move 'compute*' functions to operators/... (pytorch#65552)

Summary:
Pull Request resolved: pytorch#65552

This PR is mostly a verbatim move of several functions to different
files. The goal is to have more consistency in what resides where.

With this PR:
* All `compute*` functions defining how a given operator needs to be
lowered to TE IR will reside in `operators/*.{cpp,h}`.
* Auxiliary functions for these functions will reside in
`operators/misc.cpp`. `compute*` functions for ops not belonging
anywhere else can also go to that file.
* `operators/unary.*` is renamed to `operators/pointwise.*` and now
includes functions like `computeTwoOperands`.
* `kernel.*` now contains *only JIT-related* logic and implementations of
`TensorExprKernel` methods.

Test Plan: Imported from OSS

Reviewed By: navahgar

Differential Revision: D31148923

Pulled By: ZolotukhinM

fbshipit-source-id: e36ad8e779b8d30a33b49ea4ebf6d6a7438989f4

tools/build_variables.bzl

@@ -315,10 +315,11 @@ core_sources_full_mobile_no_backend_interface = [
     "torch/csrc/jit/tensorexpr/mem_dependency_checker.cpp",
     "torch/csrc/jit/tensorexpr/operators/conv2d.cpp",
     "torch/csrc/jit/tensorexpr/operators/matmul.cpp",
+    "torch/csrc/jit/tensorexpr/operators/misc.cpp",
     "torch/csrc/jit/tensorexpr/operators/norm.cpp",
+    "torch/csrc/jit/tensorexpr/operators/pointwise.cpp",
     "torch/csrc/jit/tensorexpr/operators/reduction.cpp",
     "torch/csrc/jit/tensorexpr/operators/softmax.cpp",
-    "torch/csrc/jit/tensorexpr/operators/unary.cpp",
     "torch/csrc/jit/tensorexpr/reduction.cpp",
     "torch/csrc/jit/tensorexpr/registerizer.cpp",
     "torch/csrc/jit/tensorexpr/tensor.cpp",