[jdk8u-dev] RFR: 8266391: Replace use of reflection in jdk.internal.platform.Metrics [v3]

[Jonathan Dowland]

> A clean backport of 8266391 for jdk8u-dev as part of cgroups v2 support.

Jonathan Dowland has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Add a macosx platform specific SystemMetrics class
 - 8266391: Replace use of reflection in jdk.internal.platform.Metrics
   
   Backport-of: 3544a9d0e4a071ad9c82aa17ab113e0101b4020b

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Changes: https://git.openjdk.org/jdk8u-dev/pull/177/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=177&range=02
  Stats: 134 lines in 5 files changed: 124 ins; 8 del; 2 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/177.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/177/head:pull/177

PR: https://git.openjdk.org/jdk8u-dev/pull/177