[master] RFR: Fix use of Klass* in GC JFR reporting [v2]

[Roman Kennke]

> Some JFR related code paths in GC access the Klass* of old objects that has already been overidden by the forwarding pointer. We can easily use the Klass* that we fetched earlier instead.
> 
> Testing:
>  - [x] tier1
>  - [x] tier2
>  - [x] jdk/jfr (some of which still fails, see subsequent PRs)

Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/hotspot/share/gc/g1/g1ParScanThreadState.hpp
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>
 - Update src/hotspot/share/gc/g1/g1ParScanThreadState.cpp
   
   Co-authored-by: Aleksey Shipilëv <shade at redhat.com>

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

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/17/files
  - new: https://git.openjdk.java.net/lilliput/pull/17/files/1bf5407f..ce81fbf9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=17&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=17&range=00-01

  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/17/head:pull/17

PR: https://git.openjdk.java.net/lilliput/pull/17