[executorch][arm] Add bfloat16 support to VGF backend

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [executorch][arm] Add bfloat16 support to VGF backend #20755

Re-land bf16 support for the Arm VGF backend, restoring the two GitHub PRs that were reverted (#20299 and #20660).

bf16 support needs the VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM VkFormat, which was added in Vulkan headers 1.4.350. The internal headers were pinned to 1.4.341, so the original diff-train import of #20299 (D110192953) failed to compile internally and both PRs were reverted in OSS. The Vulkan 1.4.350 header import and the //third-party/khronos selector wiring are the diffs below this one in the stack; this diff is the backend code that depends on them.

Changes:

• Arm backend: Add bfloat16 support to VGF backend. #20299: handle bf16 in VGFSetup.cpp (new FormatScalarKind::BFloat plus VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM cases in get_format_component_count, get_format_info, and get_format_size), the VGF test infrastructure (test_pipeline.py, runner_utils.py, test_matmul.py), and the vulkan_utils.sh SDK bump for OSS parity.
• Arm backend: Add bfloat16 to relevant vgf tests. #20660: extend bf16 test coverage across the VGF op and model tests.

All source and test changes are mirrored across the fbcode/ and xplat/ copies of the Arm backend.

Differential Revision: D110538232

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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❌ 12 New Failures, 1 Unrelated Failure

As of commit 1bcd717 with merge base 124b677 ():

NEW FAILURES - The following jobs have failed:

• pull / test-binary-size-linux-gcc / linux-job (gh)
  RuntimeError: Command docker exec -t 8f8133830f838dd581e1449bd7d29109ef6c23354ed7134a9b237534a60bd99a /exec failed with exit code 1
• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t cedda5c24929fbd92c45c1fb34800b8a4106cd1dd0b65be7e140f2dd66cbb40e /exec failed with exit code 1
• pull / unittest / windows / windows-job (gh)
  examples/models/test/test_export.py::ExportTest::test_efficient_sam_export_to_executorch
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t c56dde9503f992be59ad16e3ecb3beb3b18810cc764530877d3ddb1f647481fe /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t 70b98fa6c371c0e4d3edc9ec795694f27b5cb149783e0d110778a006d1804642 /exec failed with exit code 1
• Test ARM Backend / test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of undeclared identifier 'VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM'
• Test ARM Backend / test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of undeclared identifier 'VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM'
• trunk / test-arm-backend-vkml (test_ootb_tests_vgf) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of u
• trunk / test-arm-backend-vkml (test_pytest_models_vkml) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of undeclared identifier 'VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM'
• trunk / test-arm-backend-vkml (test_pytest_ops_vkml) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of undeclared identifier 'VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM'
• trunk / test-arm-backend-vkml (test_smaller_stories_llama_vkml) / linux-job (gh)
  /pytorch/executorch/backends/arm/runtime/VGFSetup.cpp:3704:10: error: use of undeclared identifier 'VK_FORMAT_R16_SFLOAT_FPENCODING_BFLOAT16_ARM'
• trunk / unittest-release / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 6fb4fc4a6fa02041451536d7c094b26b66de326d20fbeb39babe28aefacc10fc /exec failed with exit code 1

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-qnn-testsuite-linux / test-backend-linux (qnn, models) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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