use the //tools/codegen target in Bazel (#74465)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74465

This requires adding py_library and its PyPI dependency provider
"requirement".
ghstack-source-id: 152438643

Test Plan: Rely on CI to validate.

Reviewed By: malfet

Differential Revision: D35009795

fbshipit-source-id: 424c4968474b3c2fb37d2c7dba932b37605a63f7
(cherry picked from commit 91e442c3bf0e204b0fb6c98405aaaa7308011511)

tools/bazel.bzl

@@ -3,6 +3,13 @@ load("@rules_cuda//cuda:defs.bzl", "requires_cuda_enabled")
 load("//c10/macros:cmake_configure_file.bzl", "cmake_configure_file")
 load("//tools/config:defs.bzl", "if_cuda")
 
+def _py_library(name, **kwds):
+    deps = [dep for dep in kwds.pop("deps", []) if dep != None]
+    native.py_library(name = name, deps = deps, **kwds)
+
+def _requirement(_pypi_project):
+    return None
+
 # Rules implementation for the Bazel build system. Since the common
 # build structure aims to replicate Bazel as much as possible, most of
 # the rules simply forward to the Bazel definitions.
@@ -14,6 +21,8 @@ rules = struct(
     filegroup = native.filegroup,
     glob = native.glob,
     if_cuda = if_cuda,
+    py_library = _py_library,
+    requirement = _requirement,
     requires_cuda_enabled = requires_cuda_enabled,
     select = select,
     test_suite = native.test_suite,