[EP API] header-only adapter for EP API

[fs-eire]

Description

This PR adds a few headers for supporting building WebGPU EP and CUDA EP as plugin EPs.

See summary of #26907

[adrianlizarraga]

@fs-eire, thank you for adding these utilities. We currently have some plugin EP utilities in this directory: https://github.com/microsoft/onnxruntime/tree/main/include/onnxruntime/core/providers/utils

And there's another on the way here: #25753

Could we consolidate all of these utilities into one location?

[edgchen1]

@fs-eire, thank you for adding these utilities. We currently have some plugin EP utilities in this directory: https://github.com/microsoft/onnxruntime/tree/main/include/onnxruntime/core/providers/utils

And there's another on the way here: #25753

Could we consolidate all of these utilities into one location?

it may be worth considering whether the utility is generally useful to any plugin EP vs. useful to plugin EPs within the ORT repo. some of these seem like the latter.

[fs-eire]

@fs-eire, thank you for adding these utilities. We currently have some plugin EP utilities in this directory: https://github.com/microsoft/onnxruntime/tree/main/include/onnxruntime/core/providers/utils
And there's another on the way here: #25753
Could we consolidate all of these utilities into one location?

it may be worth considering whether the utility is generally useful to any plugin EP vs. useful to plugin EPs within the ORT repo. some of these seem like the latter.

I agree. we should not have separated implementation in different places of the repo.

In general, I think there are 2 different types of headers:

• the headers that ONLY depends on ORT public headers. This can include some useful common utils/macros and helper functions.
• the headers also depending on ORT internal headers. Specifically, for the EP adapter implementation. (currently they are in include/onnxruntime/ep/adapter)

I would recommend to put them somewhere under include/onnxruntime/, because considering the usage header-only will be much more easier for users to use. And if it's header-only, it should be put inside include/onnxruntime/.

All other details are open to discussion.