Add activation mode to com.microsoft::GatedRMSNorm for SiLU/Swish/Sigmoid across CPU, CUDA, and WebGPU

[Copilot]

Description

com.microsoft::GatedRMSNorm previously hardcoded SiLU gating; this PR keeps backward-compatible default behavior (silu) and adds explicit activation selection across CPU, CUDA, and native WebGPU.

• Schema + docs

  • Added string attribute activation to GatedRMSNorm schema with default "silu".
  • Accepted values: "silu", "swish" (alias), "sigmoid".
  • Updated operator documentation to describe both formulas.

• CPU kernel

  • Parse/validate activation during kernel construction.
  • Preserve existing FP32-intermediate RMSNorm flow and dtype coverage.
  • Apply stable gate function per mode:
    • SiLU/Swish: z * sigmoid(z)
    • Sigmoid: sigmoid(z)

• CUDA kernel

  • Parse/validate activation in host wrapper.
  • Pass a compact activation selector to LaunchGatedRMSNormKernel (no device-side string handling).
  • Keep existing launch structure, dtype registrations (float/float16/bfloat16), and FP32 arithmetic.

• WebGPU kernel

  • Parse/validate activation.
  • Specialize generated WGSL by activation mode and include mode in CacheHint to avoid shader-cache collisions.
  • Use stable sigmoid helper in both paths:
    • normalized * stable_sigmoid(z) (sigmoid)
    • normalized * (z * stable_sigmoid(z)) (silu/swish)

• Cross-EP tests (linear_attention_gates_op_test.cc)

  • Extended GatedRMSNorm test helper to take activation mode and activation attribute.
  • Added coverage for:
    • default (attribute omitted) SiLU behavior
    • explicit "silu"
    • "swish" alias parity with SiLU
    • "sigmoid" reference parity
    • float32 + float16 decode/prefill geometries
    • norm-size boundary cases
    • CUDA bfloat16 sigmoid path
    • invalid activation rejection
    • sigmoid stability with large-magnitude gate values
    • shape-validation behavior retention

OpTester tester("GatedRMSNorm", 1, onnxruntime::kMSDomain);
tester.AddAttribute<std::string>("activation", "sigmoid");  // default is "silu"

Motivation and Context

Models can require sigmoid output gating while existing ORT GatedRMSNorm was SiLU-only. This change enables both gating modes under the same operator ABI and keeps existing models behavior-identical by default.

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🟡 Changes recommended

The CUDA negative sigmoid path loses precision, its stability test cannot detect that regression, and generated operator documentation is stale.

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Review details

• Files reviewed: 10/10 changed files
• Comments generated: 3
• Review effort level: Balanced