WebGPU: Support int64 for Add operator

[huningxin]

Description

Extends the WebGPU EP Add operator to accept tensor(int64) inputs by converting its registration from a static macro to the same conditional factory-function pattern already used by Sub and Equal (#29392)

Motivation and Context

Int64 Add nodes (e.g. token-position arithmetic in LLMs, mobileclip_s0 text model) fail kernel lookup in the WebGPU EP.

The shader already handles int64 generically for all binary ops; only the kernel registration was missing the int64 type constraint for Add.

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[huningxin]

@hariharans29, PTAL, thanks!

/cc @adrastogi

[Copilot]

Pull request overview

Extends the WebGPU EP Add kernel registration to include tensor(int64) when enable_int64 is set, matching the conditional factory-function registration pattern already used for other WebGPU ops (e.g., Sub, Equal). This resolves WebGPU kernel-lookup failures for INT64 Add nodes (notably in graph-capture flows where INT64 is enabled).

Changes:

• Convert Add WebGPU kernel registration from static macro entries to conditional CreateAdd*KernelInfo(...) factory functions, registered via RegisterKernels(enable_int64).
• Add WebGPU unit tests covering INT64 Add for elementwise, broadcast, scalar LHS/RHS, and size-divisible-by-4 cases.
• Expose CreateAdd*KernelInfo declarations in binary_elementwise_ops.h for use by the WebGPU EP registry.

Show a summary per file

File	Description
onnxruntime/test/providers/cpu/math/element_wise_ops_test.cc	Adds USE_WEBGPU-guarded tests validating INT64 Add execution on WebGPU with kEnableInt64=1.
onnxruntime/core/providers/webgpu/webgpu_execution_provider.cc	Removes static Add registration and registers Add via RegisterKernels() using conditional INT64 type constraints.
onnxruntime/core/providers/webgpu/math/binary_elementwise_ops.h	Declares CreateAddVersionedKernelInfo / CreateAddKernelInfo templates for EP registration.
onnxruntime/core/providers/webgpu/math/binary_elementwise_ops.cc	Implements CreateAdd*KernelInfo and explicitly instantiates the supported versions (7–12, 13, 14+).

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Low

[huningxin]

Fixed the merge conflicts, @hariharans29, please take another look, thanks!