CI: replace JDK 15 with 16

Description

JDK 16 reached GA a few weeks ago and the natural cycle would be to replace the jobs in Quarkus CI that are currently running on JDK 15 with JDK 16. Our EA test job/workflow [1] is still running on 16 (and not 17-ea) because there are still some problems, especially with Kotlin and Gradle. The idea is to get the EA job to the point where we can make the switch (both for CI JDK 15 -> 16 and EA job 16 -> 17-ea).

[1] https://github.com/quarkusio/quarkus/actions/workflows/jdk-early-access-build.yml (see also #15867)

FTR:

• https://quarkusio.zulipchat.com/#narrow/stream/187038-dev/topic/Gradle.207
• https://quarkusio.zulipchat.com/#narrow/stream/187038-dev/topic/Quarkus.20tested.20on.20Java.2016
• https://groups.google.com/g/quarkus-dev/c/AlyXp2A2W5Y

/cc @gsmet @gastaldi

Currently known TODOs (potentially incomplete)

• fix or work around KT-43704 Illegal reflective access by com.intellij.util.ReflectionUtil to method java.util.ResourceBundle.setParent(java.util.ResourceBundle)
  • update to Kotlin 1.5 (see also: #16806)
  • or (try to) skip all Kotlin bits in the entire repo for now
  • or set --add-opens java.base/java.util=ALL-UNNAMED via MAVEN_OPTS
    • stop BootstrapMavenOptions from passing --add-opens etc. to Maven CliManager (which chokes on that), see also #16862 note: complete HACK currently (in my fork), must be done properly
• work around Gradle 6 not being compatible with JDK16+
  • don’t execute devtools/gradle and its/gradle
  • exclude anything related to Gradle from devtools/cli tests
• mitigate XStream problem in its/main: https://github.com/quarkusio/quarkus/issues/16195#issuecomment-830872415
• mitigate IAE in elytron-security-ldap: https://github.com/quarkusio/quarkus/issues/16195#issuecomment-830874787
• add workaround for Surefire java.io.tmpdir problem: https://github.com/quarkusio/quarkus/issues/16195#issuecomment-830860621
• fix inoker failures in its/container-image
• check/fix remaining “Integration Tests - Devtools” failures
• check/fix “Integration Tests - Kotlin” failures
• check/fix TCKS failures
• …?

For now checked TODOs can be found in my fork: https://github.com/quarkusio/quarkus/compare/main...famod:jdk16-fixes

[Ladicek]

Should be fixed in next SmallRye Fault Tolerance release that will contain https://github.com/smallrye/smallrye-fault-tolerance/pull/409

[Tibor17]

@famod I have removed user.dir. Let’s see the build result. https://github.com/apache/maven-surefire/tree/userDir https://ci-builds.apache.org/job/Maven/job/maven-box/job/maven-surefire/job/userDir/ The subprocess CWD and the property should have the same value. So, removing the setter for the property should not change anything but it’s safe for new versions of Java.