Move the shared reusable workflows to linux_job_v3

[huydhn]

Second of six splitting up #22107. Stacked on #22245.

_test_backend, _llm_server, _test_arduino_library, _test_cortex_m_e2e, _test_cortex_m_ops, _test_cadence and _test_riscv. Their docker-image inputs keep taking ci-image:<name>, so callers pass the same values as before.

v3 assumes role/arc through OIDC, and a reusable workflow only gets the permissions each caller hands down, so the nine test-backend-* callers of _test_backend.yml grant id-token: write.

Authored with Claude Code.

[pytorch-bot]

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✅ You can merge normally! (22 Unrelated Failures)

As of commit bd18ec6 with merge base db8b643 ():

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

• Cadence Build & Test / cpu-test / test-aot / test-aot (gh) (detected as infra flaky with no log or failing log classifier)
• Cadence Build & Test / cpu-test / test-ops / test-ops (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-arduino-library / run / arduino-library (gh) (detected as infra flaky with no log or failing log classifier)
• pull / unittest / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / unittest-buck / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / unittest-editable / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test ARM Backend / test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test ARM Backend / test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test ARM Backend / test-arm-vgf / test-backend-linux (arm_vgf_fp, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test ARM Backend / test-arm-vgf / test-backend-linux (arm_vgf_fp, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test Cortex-M Backend / test-cortex-m / test-backend-linux (cortex_m, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test NXP Backend / test-nxp / test-backend-linux (nxp_neutron_imxrt700_int8_ptq, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test OpenVINO Backend / test-openvino / test-backend-linux (openvino, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test OpenVINO Backend / test-openvino / test-backend-linux (openvino, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test QNN Backend / test-qnn / test-backend-linux (qnn, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test QNN Backend / test-qnn / test-backend-linux (qnn, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test Vulkan Backend / test-vulkan / test-backend-linux (vulkan, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test Vulkan Backend / test-vulkan / test-backend-linux (vulkan, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test WebGPU Backend / test-webgpu / test-backend-linux (webgpu, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test WebGPU Backend / test-webgpu / test-backend-linux (webgpu, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test XNNPACK Backend / test-xnnpack / test-backend-linux (xnnpack, models) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• Test XNNPACK Backend / test-xnnpack / test-backend-linux (xnnpack, operators) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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