[lilliput-jdk17u:lilliput] RFR: 8308011: [Lilliput/JDK17] Use narrow i-hash only when +UseCompactObjectHeaders

[Roman Kennke]

Currently, we use a narrow 25bit identity-hash-code in Lilliput. That is even the case when running without compact object headers, even though we could just as well use the original 31bit identity hash-code then.

The fix is relatively simple. This is a backport of https://github.com/openjdk/lilliput/pull/93. Also, this brings the code in line with what we're currently proposing in upstream https://github.com/openjdk/jdk/pull/13844.

Testing:
 - [x] tier1 +UseCompactObjectHeaders
 - [ ] tier2 +UseCompactObjectHeaders
 - [x] tier1 -UseCompactObjectHeaders
 - [ ] tier2 -UseCompactObjectHeaders

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Commit messages:
 - 8308011: [Lilliput/JDK17] Use narrow i-hash only when +UseCompactObjectHeaders

Changes: https://git.openjdk.org/lilliput-jdk17u/pull/16/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput-jdk17u&pr=16&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308011
  Stats: 61 lines in 7 files changed: 45 ins; 2 del; 14 mod
  Patch: https://git.openjdk.org/lilliput-jdk17u/pull/16.diff
  Fetch: git fetch https://git.openjdk.org/lilliput-jdk17u.git pull/16/head:pull/16

PR: https://git.openjdk.org/lilliput-jdk17u/pull/16