[lilliput-jdk21u:lilliput] RFR: 8316126: [Lilliput/JDK21] Cherry-pick: 8305895: Implementation: JEP 450: Compact Object Headers (Experimental) [v6]

[Roman Kennke]

> Let's cherry-pick the current state of upstream https://github.com/openjdk/jdk/pull/13961 into Lilliput/JDK21u.
> 
> Testing:
>  - [ ] tier1 +UCOH
>  - [ ] tier1 -UCOH

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

  Revert C2 changes

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

Changes:
  - all: https://git.openjdk.org/lilliput-jdk21u/pull/5/files
  - new: https://git.openjdk.org/lilliput-jdk21u/pull/5/files/93148bb0..f19ada4e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=5&range=05
 - incr: https://webrevs.openjdk.org/?repo=lilliput-jdk21u&pr=5&range=04-05

  Stats: 62 lines in 16 files changed: 0 ins; 36 del; 26 mod
  Patch: https://git.openjdk.org/lilliput-jdk21u/pull/5.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk21u.git pull/5/head:pull/5

PR: https://git.openjdk.org/lilliput-jdk21u/pull/5