RFR: JDK-8318636: Add jcmd to print annotated process memory map [v2]

[Thomas Stuefe]

> Analysts and supporters often use /proc/xx/maps to make sense of the memory footprint of a process.
> 
> Interpreting the memory map correctly can help when used as a complement to other tools (e.g. NMT). There even exist tools out there that attempt to annotate the process memory map with JVM information.
> 
> That, however, can be more accurately done from within the JVM, at least for mappings originating from hotspot. After all, we can correlate the mapping information in NMT with the VMA map.
> 
> Example output:
> 
> [example.system.map.txt](https://github.com/openjdk/jdk/files/13062903/example.system.map.txt)
> 
> This patch adds the VM annotations for VMAs that are *mmaped*. I also have an experimental patch that works with malloc'ed memory, but it is not ready yet for consumption and I leave that part of for now.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  start from VM op; show more thread details

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16301/files
  - new: https://git.openjdk.org/jdk/pull/16301/files/8485c1db..f3e97fac

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16301&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16301&range=00-01

  Stats: 119 lines in 6 files changed: 87 ins; 11 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/16301.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16301/head:pull/16301

PR: https://git.openjdk.org/jdk/pull/16301