[NNC] Generate C++ code for Allocate and Free (#51070)
Summary:
This is the initial skeleton for C++ codegen, it includes generations for Allocate and Free.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51070
Test Plan: New unit tests are added to `test_cpp_codegen.cpp`.
Reviewed By: ZolotukhinM
Differential Revision: D26061818
Pulled By: cheng-chang
fbshipit-source-id: b5256b2dcee6b2583ba73b6c9684994dbe7cdc1f
