[LTC] Bug fix in lazy_ir.py + code-gen softplus, softplus_backward (#66811)
Summary:
This commit fixes a bug in the codegen that was not preserving the
order of arguments when generating part of the body of the functions
in `LazyNativeFunctions.cpp`. This commit also adds codegen for
`softplus` and `softplus_backward` to test the implementation.
Test Plan:
test/cpp/build/test_ptltc --gtest_filter=AtenLtcTsTensorTest.TestSoftplus*
