Transforms: let a backend declare what counts as a permute

[rascani]

The propagation pass matched a single hardcoded target, aten.permute_copy, so a
backend carrying its own layout dialect got a pass that silently did nothing:
it never recognised the copies, so it never moved them. On the Cortex-M
explicit-layout path that is the difference between 1 cortex_m::transpose and
106, with the driver in place either way.

Take the set through the constructor. The pass still emits _PERMUTE_TARGET when
it has to create a copy, so nothing changes for a caller that does not pass the
argument, and the default is the single target it matched before.

Found by wiring the shared driver into the Cortex-M pipeline and measuring
rather than by reading: every other extension point was exercised by the Arm
suite, and this one was not, because Arm has only one permute target.

No behaviour change for Arm: the pass suite produces a failure set identical to
merge base, name for name.

Authored with Claude Code.

[rascani]

Stack from ghstack (oldest at bottom):

• -> Transforms: let a backend declare what counts as a permute #22125
• Transforms: stop fork splitting from stranding a permute #22124
• Transforms: share the permute/view propagation driver #22123
• Transforms: share the horizontal fusion passes #22122
• Transforms: share the view/permute canonicalizer #22121
• Arm backend: give the propagation pass backend extension points #22120
• Transforms: share the view/permute algebra with all backends #22119

[pytorch-bot]

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❌ 4 New Failures, 1 Cancelled Job

As of commit 627e259 with merge base e831b3e ():

NEW FAILURES - The following jobs have failed:

• pull / test-arm-backend-no-driver (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t cb85a1efaa6b4becb5e9f2d2d84973778f48f5f9c5d7247a424040585ee5be9f /exec failed with exit code 1
• pull / test-arm-backend-no-driver (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t af27825cdf18690a8a7935886569de95fd3ee12c63d8800e7b6847b7034a088e /exec failed with exit code 1
• pull / unittest-buck / linux / linux-job (gh)
  RuntimeError: Command docker exec -t be18226cdd1db7c3d07eceb7da8a55956e5c40e2074f7e4187b9bffbfcb04318 /exec failed with exit code 3
• pull / unittest-buck / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 3

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.

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