…orch#108350)

Summary:

This is a prototype for running extern fallback kernels with a host side proxy executor.

Sample of generated cpp wrapper call:
```
        at::Tensor buf0;  // output buffer
        void* tensor_args_var_0[] = {&arg0_1, &arg0_1, &arg1_1, &arg0_1, &arg1_1, &buf0};
        int64_t int_args_var_1[] = {81, 81, 7, 7, 7, 81};
        proxy_executor->call_function("buf0", int_args_var_1, tensor_args_var_0);
```

- In my current implementation, proxy executor interprets the raw pointers according to the ops schema.
This assumes that custom op MUST have a valid schema registered to Dispatcher. (I would like to validate this assumption)
- I am using callboxed() API of the custom kernels. This is inevitable, as we wish to have a single call_function API for all possible custom kernels.

- These are all the input argument types I have support so far.
       union Argument {
         # Bool value does not matter
         1: bool asNone;
         2: TensorArgument asTensor;
         3: list<TensorArgument> asTensors;
         5: i64 asInt;
         7: list<i64> asInts;
         8: double asFloat;
         9: list<double> asFloats;
         10: string asString;
         10.5: list<string> asStrings;
         11: SymIntArgument asSymInt;
         12: list<SymIntArgument> asSymInts;
         13: ScalarType asScalarType;
         14: MemoryFormat asMemoryFormat;
         15: Layout asLayout;
         16: Device asDevice;
         17: bool asBool;
         18: list<bool> asBools;
       }

- Need a policy for handling unpopulated argument with default values. Here are the options, and it has BC  implications.
1. requires exported fx graph to explicitly populate default values, if users doesn't specify.
2. requires cpp wrapper to explicitly populate default values, if fx graph doesn't specify.
3. Proxy executor look up from opSchema for default values.

For fixing T162112344

Test Plan:
frontend:
buck2 run mode/dev-sand mode/inplace -c fbcode.enable_gpu_sections=True sigmoid/frontend:export_main

test:
 buck2 run mode/dev-sand //deeplearning/aot_inductor/test:test_custom_ops


backend:
buck2 run mode/dev-nosan //deeplearning/aot_inductor/fb:main

buck2 test 'fbcode//mode/opt' fbcode//caffe2/torch/fb/model_transform/experimental/benchmark/test:test_aot_inductor_benchmark -- --exact 'caffe2/torch/fb/model_transform/experimental/benchmark/test:test_aot_inductor_benchmark - test_aot_inductor_benchmark_cmf30x (caffe2.torch.fb.model_transform.experimental.benchmark.test.test_aot_inductor_benchmark.AOTInductorBenchmark)'

Reviewed By: suo

Differential Revision: D48747417