[pkg] simplifications to broken dependency handling (#58572)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58572
Right now, we have three categories of error (broken, denied, unhandled). This
PR unifies them into a single "error" field in the node, with optional context.
It also generalizes how formatting of the error in PackagingError occurs.
Differential Revision: D28543982
Test Plan: sandcastle
Reviewed By: Chillee
Pulled By: suo
fbshipit-source-id: d99d37699ec2e172e3798763e60aafe9a66ed6f4
