[LTC] Code-gen tanh_backward (#70035)
Summary:
This commit code-generates tanh_backward. To be noted, tanh_backward
symbol is added to aten_interned_strings.h as it is missing.
Test Plan:
lazy_tensor_core/test/cpp/build/test_ptltc --gtest_filter=AtenLtcTsTensorTest.TestTanhBackward
