[BEAM-8319] Errorprone + java11 prototype, not to be merged

[lgajowy]

This configuration was tested only on sdks/java/core module. The build on openjdk11.0.2 succeeds when configured as follows:

./gradlew clean build -p sdks/java/core/ -xtest -xspotbugsMain 

Sharing this so that more people could experiment and spot potential errors or point new directions (if any).

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[stale]

This pull request has been marked as stale due to 60 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@beam.apache.org list. Thank you for your contributions.