[jdk11u-dev] RFR: 8264135: UnsafeGetStableArrayElement should account for different JIT implementation details

[Andrew Lu]

I backport this for parity with 11.0.23-oracle.

“ClassFileInstaller” path is modified as can't find jdk.test.lib.helpers.ClassFileInstaller.

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Commit messages:
 - Backport 5a930c42de276a31de94d72917425374e3bfe207

Changes: https://git.openjdk.org/jdk11u-dev/pull/2420/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2420&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8264135
  Stats: 18 lines in 1 file changed: 13 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2420.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2420/head:pull/2420

PR: https://git.openjdk.org/jdk11u-dev/pull/2420