Notes

Had to rename TrimStart & TrimEnd, as they are now implemented by Microsoft, and the behavior differs from ours.
Updates dotnet verison to dotnet9
Updates nuget packages to their respective dotnet 9 version
Had to update Umbraco.Code to 2.2 aswell, as it used the Microsoft.CodeAnalysis package, and thus we couldn't update that.

How to test

Ensure both templates & source code work with dotnet 9

Download dotnet 9 preview here: https://dotnet.microsoft.com/en-us/download/dotnet/9.0
In the root of the project, run dotnet pack -o nuget
Go to the nuget folder cd nuget
Copy the path of that folder, and then run dotnet nuget add source [PATH TO NUGET FOLDER HERE]
Install the templates, take note of the version of the templates nupkg in the nuget folder dotnet new install Umbraco.Templates::[version of templates here]
Create a new umbraco project with the new template dotnet new umbraco -n "MyTestProject"
Run the project and assert it works 👍