RFR: 8278255: add more warning text in ReentrantLock and ReentrantReadWriteLock

[Viktor Klang]

This is an attempt to be more clear about recommendations on Lock usage.

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Commit messages:
 - Adding more clarification to proper usage of locks

Changes: https://git.openjdk.org/jdk/pull/18974/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18974&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278255
  Stats: 9 lines in 3 files changed: 2 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/18974.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18974/head:pull/18974

PR: https://git.openjdk.org/jdk/pull/18974