RFR: 8367984: Eliminate offset_of in vmStructs

[Francesco Andreuzzi]

There are several usages of `offset_of` in `vmStructs`, they can be replaced with standard `offsetof` due to [JDK-8367016](https://bugs.openjdk.org/browse/JDK-8367016).

Passes `tier1`.

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Commit messages:
 - stuff

Changes: https://git.openjdk.org/jdk/pull/27362/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27362&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367984
  Stats: 20 lines in 2 files changed: 2 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/27362.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27362/head:pull/27362

PR: https://git.openjdk.org/jdk/pull/27362