[TensorExpr] Make sum available from Python (#43730)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43730
Test Plan:
python test/test_jit_fuser_te.py -k TestTEFuser.test_sum
test_tensorexpr --gtest_filter=TensorExprTest.KernelSum*
Reviewed By: ZolotukhinM
Differential Revision: D23407600
Pulled By: asuhan
fbshipit-source-id: e6da4690ae6d802f9be012e39e61b7467aa5285c
