Creating and editing slnf files from cli

[ziaulhasanhamim]

Slnf files are very useful when working on a large repository. Current creating slnf is supported from visual studio. Though it is possible to use it with cli and vs code. So why not just support creating slnf files from .net cli? Just like sln file. dotnet new slnf ....args

[marcpopMSFT]

Old issue triage: Letting copilot take a crack at this one.