RFR: 8314438: NMT: Performance benchmarks are needed to have a baseline for comparison of improvements

[Afshin Zafari]

A new benchmark for  measuring the NMT overhead in `summary` and `detail` modes.
The tests are run using: 

make CONF=debug test TEST="micro:java.util.NMTBenchmark" MICRO="RESULTS_FORMAT=json"

The results are written to a JSON file that can be visualized using [JMH Visualizer](https://jmh.morethan.io/).

### Notes
A separate [issue](https://bugs.openjdk.org/browse/JDK-8316814) is created for preparing a progfram for validating and analyzing the JMH outputs.
Another separate [issue](https://bugs.openjdk.org/browse/JDK-8316813) is created for measuring the virtual memory tracing parts of NMT.

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

Commit messages:
 - realloc and onlyMalloc are added.
 - Sequential part is run only once if WITH_THREADS == 0
 - 8314438: NMT: Performance benchmarks are needed to have a baseline for comparison of improvements

Changes: https://git.openjdk.org/jdk/pull/15563/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15563&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314438
  Stats: 254 lines in 2 files changed: 253 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15563.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15563/head:pull/15563

PR: https://git.openjdk.org/jdk/pull/15563