Improve RemovePermutesAroundElementwiseOps robustness (#18980)

[mcremon-meta]

Summary:

Improve the RemovePermutesAroundElementwiseOps pass with several
defensive enhancements:

1. Add output node boundary check: reject subgraphs where a permutable
   op feeds directly into the graph output, since removing permutes
   would silently change the output format.

2. Add constant input handling: when a subgraph boundary is a
   compile-time constant (parameter, buffer, get_attr, or ops computed
   entirely from constants), insert a compensating permute/view on it
   instead of rejecting the subgraph. This is free since it gets
   constant-folded.

3. Add clamp.default to the set of permutable ops.

4. Handle rank-mismatch for constant inputs (e.g. rank-1 bias with
   rank-4 permute) by using view_copy with appropriate shape reordering.

Reviewed By: DrJessop

Differential Revision: D101430531

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18980

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❌ 1 New Failure, 2 Unrelated Failures

As of commit 4e8cd57 with merge base 063f9c9 ():

NEW FAILURE - The following job has failed:

• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn

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

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[meta-codesync]

@mcremon-meta has exported this pull request. If you are a Meta employee, you can view the originating Diff in D101430531.

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