[executorch] Remove EXECUTORCH_CLIENTS visibility gating - Core

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #16474 by @GregoryComer
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/GregoryComer/167/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/GregoryComer/167/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/GregoryComer/167/orig
Differential Revision: D89902032
@diff-train-skip-merge

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16521

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❌ 4 New Failures, 1 Cancelled Job, 1 Pending, 7 Unrelated Failures

As of commit 70d0c88 with merge base 09b5bdb ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-arm-backend-with-no-deps (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 3b9767fe61eb895b30e2e10568ebb294dbc1885a5b08e585b1042abf2f09e199 /exec failed with exit code 127
• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_no_target) / linux-job (gh)
  RuntimeError: Command docker exec -t 2cc25d459c060e32a084339c6a79fa466f23441f348b7e7fa369ed6d9abce07b /exec failed with exit code 127
• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 69ad9b069f8d0e7fc523aeb67664d04f67eb1e8878c2aa0dc723123df991c831 /exec failed with exit code 127
• pull / unittest-arm-backend-with-no-deps (test_run_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 982dae2459ab77cbcaa5cf8f1b9031aa361e87a563c34e1526134b1737df4884 /exec failed with exit code 127

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

• Test CUDA Windows Export / export-model-cuda-windows-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / linux-job (gh)

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Test CUDA Windows Export / export-model-cuda-windows-artifact (google, gemma-3-4b-it, non-quantized) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• Test CUDA Windows Export / export-model-cuda-windows-artifact (mistralai, Voxtral-Mini-3B-2507, non-quantized) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• Test CUDA Windows Export / export-model-cuda-windows-artifact (openai, whisper-large-v3-turbo, non-quantized) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• Test CUDA Windows Export / export-model-cuda-windows-artifact (openai, whisper-large-v3-turbo, quantized-int4-weight-only) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• Test CUDA Windows Export / export-model-cuda-windows-artifact (openai, whisper-small, non-quantized) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.
• Test CUDA Windows Export / export-model-cuda-windows-artifact (openai, whisper-small, quantized-int4-weight-only) / linux-job (gh) (matched win rule in flaky-rules.json)
  ##[error]The operation was canceled.

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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