Explicit module-descriptor for Java 9 and later

[TheMrMilchmann]

What is your use-case and why do you need this feature?
As of Kotlin 1.4-M3, Java 9 module descriptors have been added to the standard library artifacts (KT-21266). It would be nice to see this also happen to libraries in the Kotlin ecosystem going forward as this would enable Kotlin JVM applications to benefit from modern JDK tools (such as jlink). As kotlinx.serialization has no remaining unmodularized dependencies, it seems like an ideal candidate to receive module support.

Describe the solution you'd like
Ideally, an explicit descriptor would be added using the Multi-Release JAR mechanism (JEP 238) added in JDK 9 (just as it was done for the standard library).

[TheMrMilchmann]

I'm currently facing a related issue with a fairly simple intermediate solution:

I would love to publish a library with an explicit module descriptor and a dependency on kotlinx.serialization but this is not possible as the latter does not have a stable module name. This could be solved by providing a stable Automatic-Module-Name entry in the JVM artifact's manifest.

[TheMrMilchmann]

Explicit module descriptors were added by #1624 and are available in 1.3.0-RC. Thanks, @lion7!