RFR: 8256383: PlatformMutex::try_lock has different semantics on Windows and Posix [v2]

[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

David Holmes has updated the pull request incrementally with one additional commit since the last revision:

  Feedback from Stefan and Thomas: prefer a check against self rather than NULL

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1247/files
  - new: https://git.openjdk.java.net/jdk/pull/1247/files/b9abcb97..e4bd2c72

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1247&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1247&range=00-01

  Stats: 6 lines in 1 file changed: 3 ins; 2 del; 1 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