[jdk21u-dev] RFR: 8340812: LambdaForm customization via MethodHandle::updateForm is not thread safe

[Goetz Lindenmaier]

I backport this for parity with 21.0.6-oracle.

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Commit messages:
 - Backport 47c10694c66bc131c8a5e1572340415b8daaba08

Changes: https://git.openjdk.org/jdk21u-dev/pull/1119/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1119&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340812
  Stats: 73 lines in 2 files changed: 70 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1119.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1119/head:pull/1119

PR: https://git.openjdk.org/jdk21u-dev/pull/1119