[executorch] Remove EXECUTORCH_CLIENTS visibility gating - Other Backends

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Devtools, Examples & More #16480
• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Extensions #16479
• -> [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Other Backends #16478
• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - XNNPACK & Vulkan Backends #16477
• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Kernels #16476
• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Runtime (backend/executor/kernel) #16475
• [executorch] Remove EXECUTORCH_CLIENTS visibility gating - Core #16474

Remove the EXECUTORCH_CLIENTS buck client list visibility gating from additional
backend targets. This replaces all visibility blocks containing @EXECUTORCH_CLIENTS
with explicit PUBLIC visibility.

This is part 5 of a multi-diff stack to remove visibility gating across all of executorch.
This diff covers:

• backends/aoti
• backends/apple (coreml, mps)
• backends/arm
• backends/cadence
• backends/cortex_m
• backends/cuda
• backends/nxp
• backends/qualcomm
• backends/test
• backends/transforms

Differential Revision: D89902029

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16478

• 📄 Preview Python docs built from this PR

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❌ 1 New Failure, 2 Unrelated Failures

As of commit d08940f with merge base 09b5bdb ():

NEW FAILURE - The following job has failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 0941f83316dbdd3ea5edb5efb1a5c5bad9a94a02927a54a87aa6b0e32bde767d /exec failed with exit code 139

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

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

• pull / unittest / macos / macos-job (gh) (trunk failure)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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