[WebGPU] Register DataTransfer to Env

[qjia7]

This pull request updates the execution provider registration logic in inference_session.cc to improve support for the WebGPU execution provider, specifically for the CopyTensors C API. The main change ensures that the WebGPU data transfer is registered not only with the session's data transfer manager but also with the environment's data transfer manager, enabling broader compatibility.

[fs-eire]

The Environment::data_transfer_mgr_ is different from InferenceSession::data_transfer_mgr_. They are the same type, but the one inside Environment should not depend on any session instance. The changes in this PR brings dependency on a specific session for Environment and I believe this is not what we want.

There is an existing method CreateAndRegisterInternalEps in class Environment, which should have already called RegisterExecutionProviderLibrary on WebGPU. Why the data transfer is not correctly registered - I can take a look at it.

[fs-eire]

Please add override CreateDataTransfer:

onnxruntime/onnxruntime/core/session/plugin_ep/ep_factory_internal_impl.h

Lines 56 to 59 in c30905d

	virtual OrtStatus* CreateDataTransfer(_Outptr_result_maybenull_ OrtDataTransferImpl** data_transfer) noexcept {
	*data_transfer = nullptr;
	return nullptr; // Default implementation does nothing
	}

in class WebGpuEpFactory (file in https://github.com/Microsoft/onnxruntime/blob/main/onnxruntime/core/session/plugin_ep/ep_factory_webgpu.h) for the purpose of this change.

[qjia7]

Please add override CreateDataTransfer:

onnxruntime/onnxruntime/core/session/plugin_ep/ep_factory_internal_impl.h

Lines 56 to 59 in c30905d

	virtual OrtStatus* CreateDataTransfer(_Outptr_result_maybenull_ OrtDataTransferImpl** data_transfer) noexcept {
	*data_transfer = nullptr;
	return nullptr; // Default implementation does nothing
	}

in class WebGpuEpFactory (file in https://github.com/Microsoft/onnxruntime/blob/main/onnxruntime/core/session/plugin_ep/ep_factory_webgpu.h) for the purpose of this change.

WebGPU DataTransfer requires a BufferManager.
For graph capture, the BufferManager is tied to the execution provider instance not session-independent. That's the problem.