RFR: 8353727: HeapDumpPath doesn't expand %p

[Kevin Walls]

This is a long-standing oversight: HeapDumpPath does not recognise %p for pid expansion.
The default filename uses a pid (e.g. java_pid1676937.hprof) but HeapDumpPath does not.
It has always done a manual "root plus pid plus extension" on the default filename only, and
should move to using Argument::copy_expand_pid() like we do with other such filenames.


We also assumed the default filename is not a directory (which is very very likely, but doesn't have to be true).

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Commit messages:
 - 8353727: HeapDumpPath doesn't expand %p

Changes: https://git.openjdk.org/jdk/pull/24482/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24482&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353727
  Stats: 73 lines in 2 files changed: 26 ins; 23 del; 24 mod
  Patch: https://git.openjdk.org/jdk/pull/24482.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24482/head:pull/24482

PR: https://git.openjdk.org/jdk/pull/24482