[AOTI] Use torchgen to generate C shim functions (#120513)
Summary: The current C shim layer manually implements a C interface for a handful of ops. Obviously that's not scalable if we want to extend it to cover all aten ops. This new torchgen script automatically generates C shim interfaces for CPU and CUDA backends. The interface follows the same parameter passing rules as the current C shim layer, such as
* Use plain C data types to pass parameters
* Use AtenTensorHandle to pass at::Tensor
* Use pointer type to pass optional parameter
* Use pointer+length to pass list
* Use device_type+device_index to pass device
* When a parameter is a pointer of pointer, e.g. AtenTensorHandle**, the script generates either a list of optional values or an optional list of values
https://gist.github.com/desertfire/83701532b126c6d34dae6ba68a1b074a is an example of the generated torch/csrc/inductor/aoti_torch/generated/c_shim_cuda.cpp file. The current version doesn't generate C shim wrappers for all aten ops, and probably generates more wrappers than needed on the other hand, but it should serve as a good basis.
This PR by itself won't change AOTI codegen and thus won't introduce any FC breakage. The actual wrapper codegen changes will come in another PR with some version control flag to avoid FC breakage.
Differential Revision: [D54258087](https://our.internmc.facebook.com/intern/diff/D54258087)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120513
Approved by: https://github.com/jansel
