RFR: 8306767: Concurrent repacking of extra data in MethodData is potentially unsafe

[Emanuel Peter]

I'm making sure that `allocate_bci_to_data` is only called when holding the `extra_data_lock`, so that no concurrent calls of it can ever occur.

Testing: tier1-3 and stress.

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Commit messages:
 - add locks for jvmci calls to allocate_bci_to_data
 - 8306767

Changes: https://git.openjdk.org/jdk/pull/16840/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306767
  Stats: 14 lines in 5 files changed: 10 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/16840.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16840/head:pull/16840

PR: https://git.openjdk.org/jdk/pull/16840