[WebGPU] Add GridSample operator

[TomCrypto]

Description

Implements the GridSample operator (opset 16–19) for the WebGPU EP.

Motivation and Context

GridSample was missing from the WebGPU EP and all other major execution providers already support it. The GridSample tests were extended to cover the WebGPU EP and seem to pass successfully.

I haven't tested that the onnxruntime-web build would pick up this new operator implementation because it's really hard to build this locally, but it seems like it should just work.

Closes #27085

[TomCrypto]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Adds initial support for the ONNX GridSample operator (opset 16–19) to the WebGPU Execution Provider, and expands existing GridSample operator tests to exercise the WebGPU EP.

Changes:

• Register GridSample (16–19) kernel for the WebGPU EP and add shader/program implementation.
• Add WebGPU EP to the GridSample provider test matrix (when USE_WEBGPU is enabled).
• Add a layout-conversion override so WebGPU doesn’t try to transform GridSample into NHWC.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
onnxruntime/test/providers/cpu/tensor/grid_sample_test.cc	Adds WebGPU EP to the set of execution providers used by GridSample tests.
onnxruntime/core/providers/webgpu/webgpu_execution_provider.cc	Registers the WebGPU GridSample kernel and disables NHWC layout conversion for this op.
onnxruntime/core/providers/webgpu/tensor/grid_sample.h	Declares the WebGPU GridSample kernel and its shader program.
onnxruntime/core/providers/webgpu/tensor/grid_sample.cc	Implements GridSample shader generation and kernel execution for WebGPU.

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[guschmue]

thanks for the op !!!