Link Vulkan backend with pybinding lib when built

[GregoryComer]

Add the Vulkan backend as a dependency to the pybinding build, when built. I've validated that I can run a simple Vulkan model on pybindings with this change on Mac (via MoltenVK).

Note that I'm not updating the preset to always build Vulkan yet. It requires additional dependencies and thus needs more discussion. I'm not sure if we can auto-install everything that we need. I'll get @SS-JIA's opinion on this. Also, once executorch::backends target is installable, I'll switch pybindings to use that target.

Tracking task: #12895.

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [Backend Tester] Seed based on test name #13313
• [Backend Tester] Reduce log verbosity / spam #13312
• [Backend Tester] Add subtest index field #13311
• -> Link Vulkan backend with pybinding lib when built #13309
• [Backend Tester] Write report progressively #13308
• [Backend Tester] Clean up report output #13306
• [Backend Tester] Clean up a few test issues #13258
• [Backend Tester] Add portable test flow #13250
• [Backend Tester] Report PTE size #13249
• [Backend Tester] Report delegation statistics #12846
• [Backend Tester] Report quantization and lowering times #12838
• [Backend Tester] Add tensor error statistic reporting #12809
• [Backend Tester] Add CSV report generation #12741
• [Backend Tester] Add Qualcomm tester and register flow #12739

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13309

• 📄 Preview Python docs built from this PR

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❌ 3 New Failures

As of commit 94d89c4 with merge base 3a02146 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
  At least one of the pre-conditions you specified did not hold
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  backends/arm/test/models/stable_diffusion/test_vae_AutoencoderKL.py::TestAutoencoderKL::test_AutoencoderKL_tosa_MI
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t 5159d9357f2cf3827d82ac007ea7b00e1818f0d5d34c9c7d3dbfef3be9cf3d14 /exec failed with exit code 1

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