[jdk21u-dev] RFR: 8331735: UpcallLinker::on_exit races with GC when copying frame anchor

[Andrew John Hughes]

Clean backport of a fix for a race condition in code adapted from `JavaCallWrapper` for the FFM API. This is more visible in 22 and later, where FFM is fully supported and the [OpenType implementation using HarfBuzz](https://bugs.openjdk.org/browse/JDK-8318364) has been ported to use it. However, the copy in the native state seems to have been introduced as far back as [JDK-8269240](https://bugs.openjdk.org/browse/JDK-8269240) in 17 when the `JavaCallWrapper` code was ported to what was then `universalUpcallHandler.cpp`.

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Commit messages:
 - Backport 461ffafeba459c077f1c2d9c5037305b71a8bc2a

Changes: https://git.openjdk.org/jdk21u-dev/pull/1424/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1424&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331735
  Stats: 15 lines in 1 file changed: 5 ins; 9 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1424.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1424/head:pull/1424

PR: https://git.openjdk.org/jdk21u-dev/pull/1424