Add affordances for quick fixing projects with NU1510

[nkolev92]

NU1510 is raised for packages that unnecessary in the project and that should be removed.
Data shows that up to 3% of pruning projects actually get warning, but don't really address despite the solution being extremely simple.

Note that given that these packages are privatized by automatically setting PrivateAssets=all and IncludeAssets=none, it's pretty much guaranteed to not have any side-effects. https://learn.microsoft.com/en-us/nuget/consume-packages/package-references-in-project-files#how-prunepackagereference-works

Some ideas here:

• PM UI visualization (example, grey out)
• Copilot fixer in error list
• Prevent installing packages that raise NU1510 warningss

[nkolev92]

Idea from @zivkan:

We should review the docs, but also we should improve the wording of the message.

PackageReference System.Text.Json will not be pruned. Consider removing this package from your dependencies, as it is likely unnecessary.

is probably too reserved.
This was created when the warning was gonna be raised per framework, as well when it wasn't privatized.
Today it's raised per project and it's privatized, so you can't even force NuGet to use this package to begin with.