Retarget to .NET 9

[rainersigwald]

Historically when we've hit releases for a new .NET version we've adopted that version. We should consider doing that for .NET 9 as well.

Items

• [x] Retarget to Arcade 9 and build dor dotnet 9 (Done: https://github.com/dotnet/msbuild/pull/10484)
• [x] Update subscriptions to Microsoft.DotNet.Arcade.Sdk from .NET ENG 8 To ".NET Eng - Latest" : Updated subscription: fc4faec0-9ee6-43b9-bc7a-08da8607f4c7
• [ ] https://github.com/dotnet/msbuild/issues/10557
• [ ] https://github.com/dotnet/msbuild/issues/9366
• [ ] https://github.com/dotnet/msbuild/issues/9720
• [ ] https://github.com/dotnet/msbuild/issues/9366
• [ ] #10576