RFR: 8287008: Improve tests for thread dumps in JSON format [v4]

[Alan Bateman]

On Mon, 23 May 2022 08:30:51 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This change is mostly test infrastructure and improvements to the testing of thread dumps in JSON format. It also tweaks the thread dump format so that the process identifier and thread identifiers are a type string rather than number.
>> 
>> The tests for thread dumps added by JEP 425 are changed to use the test infrastructure library. The tests for JEP 428 will also make use of this test infrastructure.
>
> Alan Bateman has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use string rater than number for process/thread identifiers

I've updated the patch to generating the process and thread identifiers as string rather than number (as JSON numbers that are integers don't have the required range). The test infra and DumpThreads.java test are expanded a bit and now test the processId, time and runtimeVersion fields.

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PR: https://git.openjdk.java.net/jdk/pull/8784