Inline per-tensor SIMD fast path in fusion_g3 op_dequantize (recreate D108798741)

Summary:
Recreates the optimized Fusion-G3 dequantize from D108798741, but instead of shipping it as a separate devmate kernel wired in through `operator_fallback.bzl`, it places the PDX SIMD fast path directly into the existing executorch operator `dequantize_per_tensor_out` in `executorch/backends/cadence/fusion_g3/operators/op_dequantize.cpp` (per-tensor function only; `per_channel`/`tensor`/`tensor_args` variants are untouched).

When the input and output buffers are 16-byte aligned (`dequant_simd_aligned`), the per-tensor path runs an inline PDX SIMD loop (`xb_vecMxf32`/`xb_vecMx32`/`PDX_MUL_MXF32`); otherwise it falls back to the NNLib path (`xa_nn_elm_dequantize_*`). The result is numerically identical to the original op — the same float-domain affine `(x - zero_point) * scale`.

This intentionally does NOT include the mvartanian integer-subtract change (D109458111, `PDX_SUB_MX32`); it uses the float-domain asymmetric path from D108798741 as requested. The macro fast paths (`ASYM_DEQUANTIZE_IMPL_CHANNEL`/`SYM_DEQUANTIZE_IMPL_CHANNEL`) get the `static_cast<CTYPE_OUT>((x - zp) * scale)` parenthesization required to build clean under the G3 `dev` mode's `-Werror,-Wdouble-promotion`.

For A/B measurement this also adds `op_dequantize_baseline.cpp` under the Jarvis operator test dir: a benchmark-only snapshot of the ORIGINAL executorch op (pre-SIMD, with only the `-Wdouble-promotion` fix). It defines `impl::G3::native::dequantize_per_tensor_out`, so the shared benchmark source from D109441948 is linked into two binaries — `_optimized` (against the real executorch op) and `_stock` (against the snapshot) — and compared on the cycle-accurate G3 ISS. `operators_header` visibility is extended to the Jarvis test package so the snapshot can include `operators.h`.

Differential Revision: D109500113

Author: zonglinpeng