TL;DR

Add support for Z Garbage Collector to the Graal compiler.

Goals

Add required ZGC barriers on HotSpot along with any relevant performance optimizations, allowing the use of ZGC when the Graal is used as a JIT compiler.

Non-Goals

• Add support for ZGC to GraalVM Native Image
• Add support for Shenandoah GC (although ZGC support will make it easier to support other GCs in the future)