Move selective_build.bzl to shim_et

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #14405 by @kimishpatel
^ 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/kimishpatel/198/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/kimishpatel/198/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/kimishpatel/198/orig
@diff-train-skip-merge

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14406

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures, 1 Pending

As of commit 09cd07c with merge base 654e722 ():

NEW FAILURES - The following jobs have failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 255
• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 110f62c21df376d3a7ab902c607fe50883d6058531408251e123feb39ce01cd9 /exec failed with exit code 1

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