[PyTorch] Move Aten level source list to build_variable.bzl (#52792)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52792
Move the aten level source code list from `pt_template_srcs.bzl` to `build_variables.bzl`, such that this source list can be shared by both OSS and internal.
ghstack-source-id: 122458909
Test Plan: CI
Reviewed By: dhruvbird, iseeyuan
Differential Revision: D26647695
fbshipit-source-id: 88469c934d4a73c261418c0c584e46104295a0c2
