[master] RFR: 8311875: [Lilliput] Disallow accessing oop metadata vmStructs with +UCOH

[Aleksey Shipilev]

Same as for JDK 17, but for mainline. I had to deal with some upstream reshufflings that moved the agent initialization block.

Additional testing:
 - [x] Eyeballing async-profiler initialization path in default mode and with `+UCOH`
 - [ ] Linux x86_65 fastdebug `serviceability/sa tier1 tier2`, default
 - [ ] Linux x86_65 fastdebug `serviceability/sa tier1 tier2`, `+UCOH`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/lilliput/pull/101/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=101&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311875
  Stats: 51 lines in 3 files changed: 51 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/lilliput/pull/101.diff
  Fetch: git fetch https://git.openjdk.org/lilliput.git pull/101/head:pull/101

PR: https://git.openjdk.org/lilliput/pull/101