RFR: 8327461: KeyStore getEntry is not thread-safe

[Hai-May Chao]

Change was made to engineGetEntry() in PKCS12KeyStore to extract the key and certificate chain from Entry only once. This is because the entry may get updated between engineGetKey() and engineGetCertificateChain() which causes inconsistent result. A new test was added to assess and manipulate PKCS12KeyStore with read and write operations concurrently from multiple threads. Thanks!

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Commit messages:
 - 8327461: KeyStore getEntry is not thread-safe

Changes: https://git.openjdk.org/jdk/pull/18156/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18156&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327461
  Stats: 177 lines in 2 files changed: 161 ins; 1 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/18156.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18156/head:pull/18156

PR: https://git.openjdk.org/jdk/pull/18156