[BUG] C# Dev Kit does not support .NET9 on windows

[Fluxionist]

Describe the Issue

The C# Dev Kit does not support .NET 9 on Windows.

Steps To Reproduce

Steps:

1. Install C# Dev Kit
2. .NET Install Tool is also installed
3. .NET Install Tool starts downloading .NET 8. Manually stop it.
4. Set dotnetAcquisitionExtension.sharedExistingDotnetPath to .NET 9 folder.
5. .NET Install Tool found .NET 9
6. Run command: .NET New Project...
7. Nothing happens
8. console- OUTPUT - C# Dev Kit shows the following error message:
   Starting Spawn .NET server...
   IdeBenefitsSource: Failed to fetch entitlements. Error: 'Error: Request to https://api.subscriptions.visualstudio.microsoft.com/Me/Entitlements/IDEBenefits?api-version=2023-03-26&caller=vscode failed with status code: 401 and response ""'
   Using local .NET runtime at "F:\dotnet\dotnet.exe"
   Found installed dotnet location "F:\dotnet\dotnet.exe" to load projects.
   Project system hosting process will use runtime installed in SDK.
   .NET server STDERR: You must install or update .NET to run this application.

App: c:\Users\xxx.vscode\extensions\ms-dotnettools.csdevkit-1.14.8-win32-x64\components\vs-green-server\platforms\win32-x64\node_modules@microsoft\visualstudio-server.win32-x64\Microsoft.VisualStudio.Code.Server.exe
Architecture: x64

.NET server STDERR: Framework: 'Microsoft.NETCore.App', version '8.0.0' (x64)
.NET location: F:\dotnet

The following frameworks were found:
9.0.0 at [F:\dotnet\shared\Microsoft.NETCore.App]

Learn more:
https://aka.ms/dotnet/app-launch-failed

To install missing framework, download:
https://aka.ms/dotnet-core-applaunch?framework=Microsoft.NETCore.App&framework_version=8.0.0&arch=x64&rid=win-x64&os=win10

.NET server exited with 2147516566

Expected Behavior

".NET New Project..." command should open a dialog for new project

Environment Information

Environment:

• Windows 11
• vscode 1.95.3
• .NET 9.0.0 (manually installed before this extension)
• C# Dev Kit 1.14.8 pre-release
• dotnet.exe in PATH

[webreidi]

Possibly a duplicate of #1606?

[Michael-Eng]

This is not a dup of #1606.

This bug is because our Ready2Run assemblies are built against .NET8 so we require that version of the runtime. We also have some APIs which have been deprecated in .NET9 and need to migrate.