RFR: 8267666: Add option to jcmd GC.heap_dump to use existing file [v4]

[Christoph Langer]

On Wed, 2 Jun 2021 20:57:02 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Please review a small change that adds an option to GC.heap_dump to use an existing file. 
>> 
>> The option is necessary if the target file is a predefined file-like object, like a named pipe. This opens up a lot of possibilities to process a heap dump without storing it to the file system first.
>> 
>> Reviews of the CSR linked to the bug would be appreciated as well.
>
> Anton Kozlov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix windows flags (although complied fine)

Marked as reviewed by clanger (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/4183