Backport PR #3927: Centralize SDK version in global.json

[Copilot]

Description

Backports PR #3927 from release/6.1 to release/6.0. Centralizes .NET SDK version management in global.json across all Azure DevOps pipelines.

Core Changes:

• global.json: Updated from 9.0.308 to 9.0.309, added SDK requirement documentation, changed rollForward from "latestFeature" to "latestMinor"
• New install-dotnet.yml template with useGlobalJson: true replaces hardcoded SDK versions
• ARM64 architecture support via install-dotnet-arm64.ps1

Pipeline Templates (13 files):
All CI/CD jobs now reference global.json instead of inline versions:

• Build jobs: ci-build-nugets-job.yml, ci-code-coverage-job.yml, ci-run-tests-job.yml
• Steps: ci-prebuild-step.yml, ci-project-build-step.yml, pre-build-step.yml, build-all-configurations-signed-dlls-step.yml, prepare-test-db-step.yml
• Core: dotnet-sqlclient-ci-core.yml
• Stress tests: stress-tests-ci-job.yml, stress-tests-ci-stage.yml

Additional:

• .github/workflows/codeql.yml: Uses global-json-file parameter
• BUILDGUIDE.md: Added SDK requirements section
• .editorconfig: Shell script formatting rules

Impact: Single source of truth for SDK versions, simplified pipeline maintenance, consistent rollForward behavior.

Issues

Backport of #3927.

Testing

Pipeline changes will be validated by CI runs. No functional code changes—only build infrastructure.

Guidelines

• Contributing
• Code of Conduct
• Best Practices
• Coding Style
• Review Process

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[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[paulmedynski]

Abandoning, since Copilot was unable to perform its own tasks due to errors.