RFR: 8333300: [JVMCI] add support for generational ZGC [v5]

[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.

Tom Rodriguez has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 13 commits:

 - Merge branch 'master' into tkr-genz
 - fix spelling of JVMCI
 - Merge branch 'master' into tkr-genz
 - Merge remote-tracking branch 'origin/master' into tkr-genz
 - Merge branch 'tkr-genz' of github.com:tkrodriguez/jdk into tkr-genz
 - Fix riscv compilation
 - 8333300: [JVMCI] add support for generational ZGC
 - Merge branch 'master' into tkr-genz
 - Merge branch 'master' into tkr-genz
 - Use NativeAccess to read from handles
 - ... and 3 more: https://git.openjdk.org/jdk/compare/fad6644e...b4a82828

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Changes: https://git.openjdk.org/jdk/pull/19490/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19490&range=04
  Stats: 245 lines in 16 files changed: 194 ins; 10 del; 41 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