support for bulk-updating references into csproj from commandline(s) - dotnet package update

[rrelyea]

splitting off from #3751 - which now just covers the add side of this work

Initial spec: https://github.com/NuGet/Home/blob/dev/accepted/2024/package-update-command.md

Board: https://github.com/orgs/NuGet/projects/13/views/30

[rrelyea]

since add will support "update", we'll prioritize this task as the lowest of the 4:

1. add 2) remove 3) list 4) update

[dasMulli]

Would it make sense to allow updating all package references? For a lot of dependencies, it is very quick to do sth like dotnet update pkg --all to begin with when updating a project.