Build and publish JDK specific artifacts

There are a couple ways to support publishing specific artifacts for multiple JDK versions,
* Multi-release jars (MRJARs): [https://openjdk.java.net/jeps/238](https://openjdk.java.net/jeps/238)
* Maven POM classifier: [https://maven.apache.org/pom.html#dependencies](https://www.google.com/url?q=https://maven.apache.org/pom.html%23dependencies&sa=D&ust=1601672278001000&usg=AOvVaw3rtlxhF80qaMjy8_v84CkL)

This is something that requires investigation and discussion because it isn't totally clear, to me at least, whether the benefits outweigh the costs in additional complexity (both for users and Beam committers).

Imported from Jira [BEAM-11003](https://issues.apache.org/jira/browse/BEAM-11003). Original Jira may contain additional context.
Reported by: tysonjh.

Start by reviewing the linked JEP 238 material and Maven classifier documentation, then compare multi-release JARs with classifier-based artifacts for multiple JDK versions. Define the user and committer costs, benefits, and a preferred approach before implementation; the issue currently names no files or tests.

Written by the indexing model from the issue text.