[master] RFR: 8310214: [Lilliput] Disable compact headers by default

[Aleksey Shipilev]

This would match the PRs that we eventually upstream, and would capture the tests that are failing/misbehaving without compact headers better. This would require enabling `UCOH` for testing explicitly. I took additional care to allow `@flagless` tests with `-XX:+UnlockExperimentalVMOptions -XX:+UseCompactObjectHeaders`.

Additional testing:
 - [x] Checked sample `@flagless` tests run with/without `UCOH`
 - [x] Linux x86_64 tier1, out of box
 - [ ] Linux x86_64 tier1, `-XX:+UnlockExperimentalVMOptions -XX:+UseCompactObjectHeaders`
 - [ ] Linux x86_64 tier1, `-XX:+UnlockExperimentalVMOptions -XX:-UseCompactObjectHeaders`

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Commit messages:
 - Fix
 - Disable by default

Changes: https://git.openjdk.org/lilliput/pull/99/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=99&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310214
  Stats: 7 lines in 2 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/lilliput/pull/99.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/99/head:pull/99

PR: https://git.openjdk.org/lilliput/pull/99