Add PR validation pipeline to GitHub Actions

[compulim]

Changelog Entry

Updated

• Moved pull request validation pipeline to GitHub Actions, by @compulim, in PR #4976

Description

Moving PR validation pipeline to GitHub enable community to look at how their pull request progress.

Design

Specific Changes

• Use Terrapin instead of AzDO Artifacts (npx https://aka.ms/EnableSecureFeed)
• Sharded tests into 20 shards to speed up
• Merge and report code coverage using lcov
  • Tooling (gcovr) on Cobertura is lacking on support of merging multiple XML-based coverage files
• Moved some unit tests under /__tests__/ to under their respective package path

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)