[Epic] Introducing support policy for typescript minimum version

[deyaaeldeen]

This has been discussed with the TypeScript team and our architects and we agreed to follow DefinitelyTyped's two year sliding support window.

• Discuss the support policy language With CELA and add it in
  • SUPPORT.md
  • Website
• Update Design guidelines with a reference to the support policy
• Use downlevel-dts in all packages configured to compile down to v3.8

[github-actions]

Hi @deyaaeldeen, we deeply appreciate your input into this project. Regrettably, this issue has remained inactive for over 2 years, leading us to the decision to close it. We've implemented this policy to maintain the relevance of our issue queue and facilitate easier navigation for new contributors. If you still believe this topic requires attention, please feel free to create a new issue, referencing this one. Thank you for your understanding and ongoing support.