[JIT][NNC] add hardswish symbolic gradient and NNC lowering (#57383)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57383
Notes: I picked up an activation from https://github.com/pytorch/pytorch/issues/56969. You can look at the [activations.cpp](https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/native/cpu/Activation.cpp#L429) file which has both forward and backward kernel code to help you write the NNC lowering and the symbolic gradient.
I added a test in test_jit_fuser_te for the fusion, and I added an OpInfo and asserted that we expect to see autodiffable nodes to test the symbolic gradient.
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D28197820
Pulled By: eellison
fbshipit-source-id: 05305d85c5bb0847c8f911b95ba47b137dca7e90
