Arm backend: Add TOSA PAD dialect op

[oscarandersson8218]

Adds new TOSA dialect op for PAD. aten.constant_pad_nd nodes are replaced by tosa.PAD in RewritePadPass. op_constant_pad_nd node visitor is replaced by a simpler node vistior for tosa.PAD.

cc @digantdesai @SS-JIA @freddan80 @per @zingo @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17940

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❌ 4 New Failures

As of commit 0245b20 with merge base 7824373 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t e5f34f22b6caf327d9c859dd834e05a3561d363c4516485d33212d39a9c51641 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 1617059ee33615261f014657df31cd772f09cde2865240584b522f539189bf96 /exec failed with exit code 1
• pull / unittest-editable / linux / linux-job (gh)
  examples/models/test/test_export.py::ExportTest::test_resnet18_export_to_executorch
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model

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[zingo]

Hi @SS-JIA this adds a file but I also spot srcs = glob(["op_*.py", "ops_*.py"]), so I think it should be fine.

[oscarandersson8218]

cortex_m_size_test failures are not introduced by this patch. Probably introduced by #17326.

[SS-JIA]

Should be ok!