RFR: 8256383: PlatformMutex::try_lock has different semantics on Windows and Posix

[David Holmes]

Mutex::try_lock has to allow for the possibility that the PlatformMutex::try_lock allows recursive locking.

Added additional commentary on the semantics provided by Mutex and the PlatformMutex classes.

Testing: GHA, mach5 tiers 1-3

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Commit messages:
 - 8256383: PlatformMutex::try_lock has different semantics on Windows and Posix

Changes: https://git.openjdk.java.net/jdk/pull/1247/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1247&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256383
  Stats: 18 lines in 4 files changed: 13 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1247.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1247/head:pull/1247

PR: https://git.openjdk.java.net/jdk/pull/1247