RFR: 8157023: Integrate NMT with JFR [v3]

[Stefan Johansson]

> Please review this enhancement to include NMT information in JFR recordings.
> 
> **Summary**
> Native Memory Tracking summary information can be obtained from a running VM using `jcmd` if started with `-XX:NativeMemoryTracking=summary/detail`. Using `jcmd` requires you to run a separate process and to parse the output to get the needed information. This change adds JFR events for NMT information to enable additional ways to consume the NMT data.
> 
> There are two new events added:
> * _NativeMemoryUsage_ - The total native memory usage.
> * _NativeMemoryUsagePart_ - The native memory usage for each component.
> 
> These events are sent periodically and by default the interval is 1s. This can of course be discussed, but that is the staring point. When NMT is not enabled on events will be sent.
> 
> **Testing**
> * Added a simple test to verify that the events are sent as expected depending on if NMT is enabled or not.
> * Mach5 sanity testing

Stefan Johansson has updated the pull request incrementally with one additional commit since the last revision:

  Special snapshot for NMT events in JFR

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11449/files
  - new: https://git.openjdk.org/jdk/pull/11449/files/57ab6576..04017864

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11449&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11449&range=01-02

  Stats: 263 lines in 5 files changed: 200 ins; 26 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/11449.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11449/head:pull/11449

PR: https://git.openjdk.org/jdk/pull/11449