Upgrade to .NET 9.0

[Arlodotexe]

This PR updates our tooling to .NET 9.0.100, including updates to:

• TargetFrameworks
  • Added alongside existing TFMs for Uno and Wasdk
  • Update tooling to handle multi-tfm value for Uno
• Dockerfile and devcontainer (used by VS Code, locally & Codespaces)
• GitHub Actions CI (build.yml)
• global.json (selects dotnet version used by runtime)
• Dependent packages (Uno Platform)
• Misc error fixes in components for net9.0.

Prerequisite PR: https://github.com/CommunityToolkit/Tooling-Windows-Submodule/pull/230