RFR: 8357650: ThreadSnapshot to take snapshot of thread for thread dumps [v3]

[Alex Menkov]

> This is first (hotspot) part of the update for `HotSpotDiagnosticMXBean.dumpThreads` and `jcmd Thread.dump_to_file` to include lock information in thread dumps (JDK-8356870).
> The update has been split into parts to simplify reviewing.
> The fix contains an implementation of `jdk.internal.vm.ThreadSnapshot` class to gather required information about a thread.
> Second (dependent) part includes changes in `HotSpotDiagnosticMXBean.dumpThreads`/`jcmd Thread.dump_to_file`, spec updates and tests for the functionality.
> 
> Testing: new `HotSpotDiagnosticMXBean.dumpThreads`/`jcmd Thread.dump_to_file` functionality was tested in loom repo;
>   sanity tier1 (this fix only)

Alex Menkov has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'openjdk:master' into thread_dump
 - move to ThreadService
 - initial fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25425/files
  - new: https://git.openjdk.org/jdk/pull/25425/files/77489f3a..ce7d4fa3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25425&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25425&range=01-02

  Stats: 29059 lines in 599 files changed: 20212 ins; 5748 del; 3099 mod
  Patch: https://git.openjdk.org/jdk/pull/25425.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25425/head:pull/25425

PR: https://git.openjdk.org/jdk/pull/25425