FasterTransformer model wrapper using custom op (#15013)
### Description
<!-- Describe your changes. -->
We are introducing the FasterTransfomer model-level integration using
ORT [custom op runtime
wrapper](https://github.com/microsoft/onnxruntime/pull/13427).
In order to make the FT wrapper/integration work, two things need to be
done:
- New API `KernelInfoGetConstantInput_tensor`. (Done in this PR)
During custom op kernel initialization, it needs to get the model
weights (saved as node's constant inputs) ready for FT's weights
instantiation. What's why we need to add this new API to make kernel
info capable of getting constant inputs.
- Custom op and custom op kernel to wrap FT model. (Will provide in
onnxruntime extensions or inference examples)
During custom op kernel initialization, it can fetch attributes from
kernel info to determine which kind of FT model instance create. During
custom op kernel compute/inference, it can get input/output from kernel
context and then assign input/output buffers for model instance to run.
