Arm Backend: Add support for select_scatter.default

[agrima1304]

Add tests for the select_scatter.default op and decompose it into other operators. The decomposition only needs to occur in the INT pipeline since it is already supported in the FP pipeline, where it is decomposed during the export stage.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 2 New Failures, 1 Unrelated Failure

As of commit f8c877f with merge base 4860984 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-editable / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn
• trunk / test-mcu-cortex-m-backend / linux-job (gh)
  RuntimeError: Command docker exec -t 2247f43c554fe4f5fa87bf20d7deecb473ecbddc4e45cbef9808041763ee8ccc /exec failed with exit code 1

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Apple / build-demo-ios / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 74

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