.Net upgrade to 9.0

[elinohlsson]

Is your feature request related to a problem? Please describe.
Upgrade .NET version to 9.0

[ivara]

IMPORTANT

There is an issue in .NET 9 (9.0.101) that seems to prevent this upgrade
dotnet/runtime#110067

Pretty hefty diagnostics done by Nness in this comment
dotnet/runtime#110067 (comment)