javadoc-plugin no longer builds the project's "api-javadoc" and "full-javadoc".
The move from jdk-8 apis to jdk-9+ (i.e. jdk-11+) apis has resulted in a failure
to resolve jdk class references. In addition the current maven-javadoc-plugin version
is 3.0.1. This version is 6 years out of date. The current plugin version is
3.7.0. Elytron should be upgraded to the current version. In doing this
an additional configuration dependencies (e.g. <additionalDependencies>)
element must be added to the plugin's defintion in order for 3rd party
class references to be resolved and thus enable the site files to be generated.