[ExecuTorch][WebGPU] Preserve Linear and Q4 embedding params across dynamic resize

[JCNTH]

Stack from ghstack (oldest at bottom):

• -> [ExecuTorch][WebGPU] Preserve Linear and Q4 embedding params across dynamic resize #21482
• [ExecuTorch][WebGPU] Generate logical and arithmetic binary shader variants #21451
• [ExecuTorch][WebGPU] Generate extrema and unary shader variants #21450
• [ExecuTorch][WebGPU] Generate typed to_copy shader variants #21449
• [ExecuTorch][WebGPU] Make WGSL generation rollback-safe #21448
• [ExecuTorch][WebGPU] Add Qwen3 K16 attention and fp16 KV cache #21136
• [ExecuTorch][WebGPU] Add HuggingFace rotate-half RoPE #21135
• [ExecuTorch][WebGPU] Repair dynamic SDPA routing, add attestation #21134
• [ExecuTorch][WebGPU] Select emdawnwebgpu for Emscripten builds #21133
• [ExecuTorch][WebGPU] Add Llama K16 online causal attention #21132
• [ExecuTorch][WebGPU] Replace broad QKV fusion with BK64 kernel #21131
• [ExecuTorch][WebGPU] Route exact prefill shapes to the BK64 GEMM #21130
• [ExecuTorch][WebGPU] Fuse the SwiGLU elementwise chain #21129
• [ExecuTorch][WebGPU] Coordinate dynamic dispatch routes #21128
• [ExecuTorch][WebGPU] Add certified scoped output suppression #21127

Preserve immutable Linear and Q4 embedding shader controls across dynamic resize through typed parameter authorities.

Problem
The Linear resize hook dropped has_bias, and the Q4 embedding resize path could drop is_linear_weight. Both defects produced correct build-time outputs but silently changed semantics after a live shape update.

Solution

• Before: build and resize populated control words independently, allowing immutable shader state to reset.
• After: each build/resize pair calls one typed helper while recomputing only live counts and dispatch.

Implementation

• Linear.cpp — make_linear_params preserves the bias flag across vec4 and tiled routes.
• EmbeddingQ4gsw.cpp — EmbeddingLayout and make_embedding_params preserve nibble layout across resize.
• Mirrors Vulkan runtime/graph/ops/impl/Linear.cpp and EmbeddingQ4gsw.cpp, which carry immutable shader controls through dynamic dispatch.

Constraints
WGSL bytes, shader selection, bindings, uniform sizes, queue-write counts, dispatch formulas, and pipeline topology are unchanged. Production handler code is smaller because duplicated field population and scalar captures are removed.

Co-authored-with: Claude Code.

Differential Revision: D113992326

[pytorch-bot]

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