Address remaining JSR-305 annotations

[epkugelmass]

The (partial) transition from "JSR-305" nullability annotations to Checker Framework annotations in 23.6 [1] was a welcome change. However, the remaining JSR-305 annotation usages like "package-level" nullability default [2] make it difficult for FindBugs users to use Guava >= 23.6. FindBugs does not recognize the new Checker Qual annotations and so reasons that null-tolerant methods like ToStringHelper::add(String, @org.checkerframework.checker.nullness.qual.Nullable Object) are actually null-intolerant.

Given that null-intolerance is the default the Checker type system, and also given the open task [3] to remove the JSR-305 dependency entirely, would Guava consider removing usages of javax.annotation.ParametersAreNonnullByDefault and friends in the next release?

[1] https://github.com/google/guava/releases/tag/v23.6
[2] https://github.com/google/guava/blob/master/guava/src/com/google/common/base/package-info.java#L59
[3] #2960

[cgdecker]

Marking as a duplicate of #2960 which is still open for tracking this issue. AFAIK we still need Jetbrains to do something so that we won't break Kotlin users by migrating away from @ParametersAreNonNullByDefault.

@cpovirk in case there's something here you want to note in the other issue.