RFR: 8318026: jcmd should provide access to detailed JVM object information [v12]

[Kevin Walls]

> Introduce the jcmd "VM.inspect" to implement access to detailed JVM object information.
> 
> Not recommended for live production use.  Requires UnlockDiagnosticVMOptions and not included in jcmd help output, to remind us this is not a general-purpose customer-facing tool.

Kevin Walls 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 26 additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into 8318026_jcmd_VMdebug_command
 - One dbg_is_good_oop method
 - Test more pointer types: compiled method and metadata.
 - Argument to be named address.
 - test nit
 - Undo include
 - Change to jcmd VM.inspect
 - Merge remote-tracking branch 'upstream/master' into 8318026_jcmd_VMdebug_command
 - Test update
 - Show description if unknown subcommand.
 - ... and 16 more: https://git.openjdk.org/jdk/compare/ca24041f...e7fc0325

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17655/files
  - new: https://git.openjdk.org/jdk/pull/17655/files/9ed958f6..e7fc0325

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17655&range=11
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17655&range=10-11

  Stats: 13189 lines in 329 files changed: 4768 ins; 6005 del; 2416 mod
  Patch: https://git.openjdk.org/jdk/pull/17655.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17655/head:pull/17655

PR: https://git.openjdk.org/jdk/pull/17655