quirk needed for t64 library transitions in 24.04

[Steve Langasek]

As of right now, https://ubuntu-archive-team.ubuntu.com/nbs.html still has a very long list of packages that need cleaned up before we release 24.04 LTS in 2 weeks, and none of these packages are considered candidates for removal yet due to reverse-dependencies.

Most of these reverse-dependencies are amd64-only dependencies on pre-t64 library packages, due to the fast and highly-parallelized rebuild of packages in response to xz-utils.

The good news is that, because these libraries are ABI-compatible on amd64 and declare so via Provides:, the amd64 packages are not uninstallable if we remove these libraries.

The bad news is, on upgrade from prior releases, apt will not know to replace the non-t64 library with the t64 library if the user has no packages installed that depend on the t64 library name; leaving them islanded on library versions that are installable and compatible, but not security supported in 24.04.

In order to handle this without doing no-change rebuilds of all of those reverse-dependencies (which we simply do not have time for before release), Julian points out that it's possible for us to quirk things to ensure the libraries are swapped on upgrade:

- for each installed package
  - if the package is no longer available, and there is a package which Replaces+Provides+(Conflicts|Breaks) that package, mark it for install

this should handle all of the t64 library transitions, and should also be safe against accidentally switching users to a different implementation of a package than the one they want to keep.