Prioritize the most recent version of a package

[jakemac53]

When loading AI assets from packages in a workspace with multiple package roots, we can have multiple versions of a package present.

The initial implementation just loads in the first version we see, and ignores future ones. This should instead load the most recent one, as that is most likely the best one.

[jakemac53]

See prior art in DevTools https://github.com/flutter/devtools/blob/master/packages/devtools_app/lib/src/extensions/extension_service_helpers.dart