Rework the NU1510 heuristic, only raise it when a package id can be completely removed from the project

[nkolev92]

Bug

Related: NuGet/Home#14196

Description

Spec: NuGet/Home#14325

This captures the first part which was something we reviewed with partners during earlier discussion.
https://github.com/NuGet/Home/blob/dev-nkolev92-packagepruning-directrefs/accepted/2025/PrunePackageReference-with-direct-PackageReference.md#how-do-we-tell-the-customers-we-want-them-to-remove-a-packagereference

The part about direct pruning is still a work in progress.

• Remove the raising of NU1510 from the resolver code. This is something that can be calculated independent of the resolved graph.
• By moving this logic out of the core resolver code, it allows us to more easily make decisions based on multiple frameworks.

PR Checklist

• Meaningful title, helpful description and a linked NuGet/Home issue
• Added tests
• Link to an issue or pull request to update docs if this PR changes settings, environment variables, new feature, etc. - Update the NU1510 documentation Home#14330