Use of service loader in describe.kt is not threadsafe

[daviddenton]

When running tests in parallel, we are seeing threading problems with the following line of code:
private val descriptionServices = ServiceLoader.load(ValueDescription::class.java)

https://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html says “Instances of this class are not safe for use by multiple concurrent threads.”

[npryce]

Fix committed and published to Maven Central