RFR: 8371083: FollowReferences reports non-class objects as JVMTI_HEAP_REFERENCE_SYSTEM_CLASS [v2]

[Alex Menkov]

> FollowReferences with null initial_object starts heap walking from "heap roots", which include system classes.
> All oops from ClassLoaderDataGraph are reported with JVMTI_HEAP_REFERENCE_SYSTEM_CLASS kind, but some of the objects are not classes.
> The fix updates FollowReferences to report non-class objects from ClassLoaderDataGraph as JVMTI_HEAP_REFERENCE_OTHER
> 
> Testing: tier1..4,hs-tier5-svc

Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:

  feedback

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28224/files
  - new: https://git.openjdk.org/jdk/pull/28224/files/1ee62064..efa0b538

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28224&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28224&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28224.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28224/head:pull/28224

PR: https://git.openjdk.org/jdk/pull/28224