RFR: 8304074: [JMX] Add an approximation of total bytes allocated on the Java heap by the JVM [v15]

[Paul Hohensee]

> Please review this addition to com.sun.management.ThreadMXBean that returns the total number of bytes allocated on the Java heap since JVM launch by both terminated and live threads.
> 
> Because this PR adds a new interface method, I've updated the JMM_VERSION to 4, but would be happy to update it to 3_1 instead.

Paul Hohensee has updated the pull request incrementally with one additional commit since the last revision:

  8304074: Define FULL_MEM_BARRIER for linux_arm

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13814/files
  - new: https://git.openjdk.org/jdk/pull/13814/files/5515fc59..4ce0ede7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13814&range=14
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13814&range=13-14

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13814.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13814/head:pull/13814

PR: https://git.openjdk.org/jdk/pull/13814