Move off JSR-305 annotations

[graemerocher]

See spotbugs/spotbugs#421

The JSR-305 from findbugs is not longer supported, has split package problems for Java 9+ and may represent an Oracle license violation.

We currently use javax annotations for Nullable and Nonnull we need to eliminate the use of these annotations directly but still support them via annotation mapping.

The following screenshot shows the currently supported annotations by IntelliJ out of the box:

Google tools are moving to the Checker Framework so maybe we should use that since it is supported out of the box by IntelliJ

The other option is our own set of annotations, however that would require end users to configure IntelliJ (and any other tooling) explicitly.

[graemerocher]

See also micronaut-projects/micronaut-examples#45

[graemerocher]

Checker framework seems massive and also repackages javax.annotation classes. I think probably https://github.com/spotbugs/spotbugs/tree/master/spotbugs-annotations/src/main/java/edu/umd/cs/findbugs/annotations are the best ones to migrate to

[sdelamo]

Kotlin supported nullability annotations: https://kotlinlang.org/docs/reference/java-interop.html#nullability-annotations