[ET-VK] Move operator specific quantize/dequantize ops to QuantizeDequantize.cpp

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK] Re-implement (de)quantize_per_tensor.default #15721
• [ET-VK] Rename quantize/dequantize functions/shaders to be more generic #15720
• -> [ET-VK] Move operator specific quantize/dequantize ops to QuantizeDequantize.cpp #15707
• [ET-VK][ez] Deprecate quantized_decomposed op implementations #15706
• [ET-VK] Implementation of gather #15705
• [ET-VK][ez] Constrain out repsets individually #15704
• [ET-VK] Allow buffer input/output for quantize/dequantize for conv2d ops #15703
• [ET-VK][ez] Apply quantize op replacement to all argument nodes #15702

Title says it all! This diff is mostly just moving code around for better organization. Specifically, functions that handle quantizing / dequantizing tensors are placed in a new file QuantizeDequantize.cpp.

Differential Revision: D86674168

[pytorch-bot]

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❌ 5 New Failures

As of commit 046dc63 with merge base aba44fd ():

NEW FAILURES - The following jobs have failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 4e8a33f5e169be6934974213276b9b5a52d282e1da1aee7de239747ce4a8ae5f /exec failed with exit code 139
• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest / macos / macos-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / linux / linux-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_int8_static_quant_recipe

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