RFR: 8261251: Shenandoah: Use object size for full GC humongous compaction

[Roman Kennke]

Currently, copying objects in full GC humongous object comaction copies the full region. We can limit that to copying only the object size and save some wasted cycles. Also, this fixes a test failure with loom where object copy checks that the given size matches the object size.

 - [x] hotspot_gc_shenandoah
 - [ ] tier1(+Shenandoah)

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Commit messages:
 - 8261251: Shenandoah: Use object size for full GC humongous compaction

Changes: https://git.openjdk.java.net/jdk/pull/2433/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2433&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261251
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2433.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2433/head:pull/2433

PR: https://git.openjdk.java.net/jdk/pull/2433