[Copilot]

Description

This PR expands com.microsoft contrib-op support needed by the Qwen4-Exp / Qwen3.8-Flash-Next text architecture, focused on Engram gating and n-gram hash mapping. The GatedRMSNorm activation-mode changes were removed from this PR and are now covered separately by #32512.

Changes include:

• EngramGate: add optional conv_norm_scale input and optional gated_value_normed output for the normalized gated-value path.
• NGramHashMapping: add autoregressive decode and packed-sequence support with optional past_ids, present_ids, head_offsets, eos_token_id, segment_ids, and reset_on_eos behavior.
• CPU, CUDA, and WebGPU implementations for the retained EngramGate and NGramHashMapping behavior.
• Generated contrib operator/kernel documentation for the retained schema and kernel changes.
• Extended contrib-op tests covering CPU/CUDA/WebGPU behavior, in-place state handling, packed sequences, EOS reset behavior, and EngramGate normalized output.

Motivation and Context

Qwen4-Exp requires n-gram embeddings and Engram-style gating variants that were not fully covered by the existing contrib operators. This PR extends the relevant operators incrementally while preserving prior behavior by default.

GatedRMSNorm sigmoid/activation support is intentionally excluded here so that it can be reviewed and merged via #32512.

[azure-pipelines]

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