RFR: JDK-8176520: Improve the accuracy of the instance size in hprof heap dumps [v3]

[Alex Menkov]

> The fix updates heap dumpers to report correct instance size value for HPROF_GC_CLASS_DUMP records (currently it's reported as size of all instance fields)
> 
> Testing: tier1, tier2, tier5-svc

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

  split test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17855/files
  - new: https://git.openjdk.org/jdk/pull/17855/files/abba6396..2a5626d6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17855&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17855&range=01-02

  Stats: 137 lines in 2 files changed: 126 ins; 1 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/17855.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17855/head:pull/17855

PR: https://git.openjdk.org/jdk/pull/17855