[ExecuTorch][WebGPU] et_vk.apply_rotary_emb test suite (export + native golden)

[JulianCloudNTH]

Stack from ghstack (oldest at bottom):

• [ExecuTorch][WebGPU] et_vk.prepack test suite (export + native golden) #20292
• [ExecuTorch][WebGPU] Add et_vk.prepack (constant-tensor packing) for E2E weight loading #20265
• -> [ExecuTorch][WebGPU] et_vk.apply_rotary_emb test suite (export + native golden) #20290
• [ExecuTorch][WebGPU] Add et_vk.apply_rotary_emb (interleaved RoPE) + ValueList multi-output #20264
• [ExecuTorch][WebGPU] et_vk.embedding_q4gsw test suite (export + native golden) #20289
• [ExecuTorch][WebGPU] Add et_vk.embedding_q4gsw (4-bit groupwise-symmetric quantized embedding) #20263

Splits the et_vk.apply_rotary_emb tests into their own diff (op below, tests above), matching the sdpa/update_cache/linear_q4gsw convention, and brings them to the same rigor: a multi-shape config sweep run on-device (prefill + decode) and a library dual-oracle at both shapes.
@exported-using-ghexport

Differential Revision: D108668384

Differential Revision: D108668384

[pytorch-bot]

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⏳ 1 Pending, 1 Unrelated Failure

As of commit 609b39b with merge base 0378fc4 ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-qnn-delegate-linux / linux-job (gh) (trunk failure)

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