RFR: 8252842: Extend jmap to support parallel heap dump [v32]

[David Holmes]

On Tue, 21 Sep 2021 02:07:39 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> I will start reviewing this today.
>
> Thanks @schmelter-sap and @plummercj for your help review and approve this PR!
> Since this is a non-trivial change, I would like to wait for 2 days before integrate it in case more comments from others.

@linzang  this change is causing test crashes on Windows with ZGC and EpsilonGC - please see JDK-8274196

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

PR: https://git.openjdk.java.net/jdk/pull/2261