RFR: 8255414: Ensure OS functions always report to NMT

[Johan Sjölen]

Hi,

This PR attempts to enforce the convention that:

1. Public `os` functions report to NMT
2. `pd_` prefixed functions do not report to NMT
3. Public `os` functions call into `pd_`-prefixed functions to do the actual work.

This is a convention that has been only partially enforced, leading to some difficulties. For example, it's easy for double-accounting to NMT can occur if it's not clear what the `pd_`-prefixed functions do and do not do.

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Commit messages:
 - Merge remote-tracking branch 'origin/master' into 8255414-separate-pd-os
 - Do not use unadorned os function in pd_-adorned function

Changes: https://git.openjdk.org/jdk/pull/12832/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12832&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8255414
  Stats: 46 lines in 8 files changed: 15 ins; 0 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/12832.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12832/head:pull/12832

PR: https://git.openjdk.org/jdk/pull/12832