RFR: JDK-8327769: jcmd GC.heap_dump without options should write to location given by -XX:HeapDumpPath, if set

[Matthias Baesken]

Currently jcmd command GC.heap_dump only works with an additionally provided file name.
Syntax : GC.heap_dump [options] <filename>

In case the JVM has the XX - flag HeapDumpPath set, we should support an additional mode where the <filename> is optional.
In case the filename is NOT set, we take the HeapDumpPath (file or directory);

new syntax :
GC.heap_dump [options] <filename> .. has precedence over second option
GC.heap_dump [options] …in case -XX: HeapDumpPath=p is set

This would be a simplification e.g. for support cases where a filename or directory is set at JVM startup with -XX: HeapDumpPath=p and writing to the path is intended/recommended for usage also in the jcmd case.

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Commit messages:
 - JDK-8327769

Changes: https://git.openjdk.org/jdk/pull/18190/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18190&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327769
  Stats: 190 lines in 3 files changed: 113 ins; 68 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/18190.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18190/head:pull/18190

PR: https://git.openjdk.org/jdk/pull/18190