Build the project with the latest JDK (14 in this timing) with https://github.com/java9-modularity/gradle-modules-plugin
to make sure we can run tests with Java 9 or later. refs #1136 for example.

This change won't affect the version of .class files (we keep using Java 8 to compile), however, the JPMS support could be updated in this change from using META-INF to package-info.java.

refs #1123