RFR: 8277444: Race condition on Instrumentation.retransformClasses() and class linking

[Evgeny Astigeevich]

There is a race between `JvmtiClassFileReconstituter::copy_bytecodes` and `InstanceKlass::link_class_impl`.  `InstanceKlass::link_class_impl` can be rewriting bytecodes. `JvmtiClassFileReconstituter::copy_bytecodes` will not restore them to the original ones because the flag `rewritten` is `false`. This will result in invalid bytecode.

This PR adds a lock (`init_lock`) to the `copy_bytecodes` method to prevent reading bytecodes while they are being rewritten during class linking.

Tested fastdebug and release builds: Linux x86_64 and arm64
- The reproducer from JDK-8277444 passed.
- Tier1 - tier3 passed.

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Commit messages:
 - 8277444: Race condition on Instrumentation.retransformClasses() and class linking

Changes: https://git.openjdk.org/jdk/pull/26863/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26863&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8277444
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26863.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26863/head:pull/26863

PR: https://git.openjdk.org/jdk/pull/26863