RFR: 8333300: [JVMCI] add support for generational ZGC

[Tom Rodriguez]

This exposes the required values for JVMCI to support generational ZGC.  It includes a few things worth mentioning.  JVMCI still exports XBarrierSetRuntime as fields in CompilerToVM::Data under the original name of ZBarrierSetRuntime.  I have exported the XBarrierSetRuntime and ZBarrierSetRuntime functions as addresses under their actual name.  This permits backward compatibility until all the required parts are in place.  We can eventually delete the CompilerToVM::Data names.

I added ZBarrierSetRuntime::load_barrier_on_oop_array paralleling XBarrierSetRuntime::load_barrier_on_oop_array as we use that for a vector barrier.  I could create the function as part of JVMCIRuntime if there are any concerns about including that in the ZGC core.

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Commit messages:
 - 8333300: [JVMCI] add support for generational ZGC

Changes: https://git.openjdk.org/jdk/pull/19490/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19490&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333300
  Stats: 241 lines in 14 files changed: 193 ins; 10 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/19490.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19490/head:pull/19490

PR: https://git.openjdk.org/jdk/pull/19490