[jdk16u] RFR: 8261251: Shenandoah: Use object size for full GC humongous compaction

[Aleksey Shipilev]

This fixes a minor performance issue in Shenandoah (which becomes asserted in later projects, i.e. Loom).

Additional testing:
 - [x] hotspot_gc_shenandoah

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

Commit messages:
 - Backport deb0544ff330fadc5aac0378766bcd36c220d7e2

Changes: https://git.openjdk.java.net/jdk16u/pull/55/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=55&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/jdk16u/pull/55.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/55/head:pull/55

PR: https://git.openjdk.java.net/jdk16u/pull/55