FR: Gazelle resolve class directives about rules_jvm HOT 1 OPEN

In general, I think doing class rather than package based resolution where we can makes sense. I say where we can because we can't always reliably do so, the major exceptions that come to mind are:

1. Generated code - both from things like annotation processers, and from things like protoc - we can't reliably know what classes some code may generate.
2. Third party libraries - we rely on rules_jvm_external's lockfile which indexes a list of packages (e.g. in this example) - while we could have rules_jvm_external list out every class in every jar, that would make the lockfile huge (and also very churn-y when versions change).

Right now in our code, we treat packages and classes interchangeably quite often - #153 is a step towards not doing that so much - it introduces specific types for packages and classes, and makes clear where each is being used. It also documents that this gazelle plugin assumes quite strongly that people follow standard java naming conventions. Once that lands, I think being able to support class-specific resolves, even without doing general class-based resolution and keeping with packages as the primary resolution key, would be quite simple.

from rules_jvm.