Arm backend: Update VGF test for fused ReLU qparams

[JacobSzwejbka]

Update the VGF rewrite-convolution regression for the ReLU fusion behavior introduced by D116922192.

The ReLU is fused into the convolution before ConvertToClampPass runs, so the clamp is fused away and no clamp node remains. Verify that the fused convolution owns the output quantization parameters with qmin rewritten to the zero point.

Rename the adjacent lowering test to describe the fused Conv-ReLU-Cat path.

Test plan:

• buck test @fbcode//mode/dev fbcode//executorch/backends/arm/test:rewrite_conv_pass -- --exact "fbcode//executorch/backends/arm/test:rewrite_conv_pass - test_rewrite_conv_pass.py::test_fold_and_annotate_q_params_vgf_quant_tracks_fused_relu_qparams"
• buck test @fbcode//mode/dev fbcode//executorch/backends/arm/test:rewrite_conv_pass -- --exact "fbcode//executorch/backends/arm/test:rewrite_conv_pass - test_rewrite_conv_pass.py::test_rewrite_conv_vgf_quant_handles_fused_conv_relu_cat_branch" "fbcode//executorch/backends/arm/test:rewrite_conv_pass - test_rewrite_conv_pass.py::test_rewrite_conv_vgf_quant_infers_quantized_bias_dtype_from_inputs"
• arc lint -a and arc lint on changed files
• python -m py_compile backends/arm/test/passes/test_rewrite_conv_pass.py

This PR was authored with Codex.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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[zingo]

nit: The updated fused-ReLU coverage looks correct. As a follow-up, would it
make sense to retain a separate non-fusible Conv-Clamp case? The original
test protected that path for #18778, and this change repurposes its only
regression coverage.