[master] RFR: Preserve Klass* in leak profiler [v2]

[Roman Kennke]

> The JFR leak profiler uses the mark word for marking objects during traversal, and for storing pointers to Edges. We need to preserve the compressed Klass* in the upper part of the mark-word during the traversal.
> 
> The change is based on: openjdk/jdk/pull/5918
> 
> Testing:
>  - [x] jdk/jfr (x86_64)
>  - [x] jdk/jfr (x86_32)
>  - [x] tier1
>  - [x] tier2

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Cherry-pick  8275277: assert(dest_attr.is_in_cset() == (obj->forwardee() == obj)) failed

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Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/21/files
  - new: https://git.openjdk.java.net/lilliput/pull/21/files/c1368efb..a49c72e1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=21&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=21&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/21/head:pull/21

PR: https://git.openjdk.java.net/lilliput/pull/21